Technical Support

Technical Support icon

OSC Help consists of technical support and consulting services for OSC's high performance computing resources. Members of OSC's HPC Client Services group comprise OSC Help.

Before contacting OSC Help, please check to see if your question is answered in either the FAQ or the Knowledge Base. Many of the questions asked by both new and experienced OSC users are answered in these web pages.

If you still cannot solve your problem, please do not hesitate to contact OSC Help:

Toll Free: (800) 686-6472
Local: (614) 292-1800
Email: oschelp@osc.edu
Submit your issue online

OSC Help hours of operation:

Basic and advanced support are available Monday through Friday, 9 a.m.–5 p.m., except OSU holidays

OSC users also have the ability to directly impact OSC operational decisions by participating in the Statewide Users Group. Activities include managing the allocation process, advising on software licensing and hardware acquisition.

We recommend following HPCNotices on Twitter to get up-to-the-minute information on system outages and important operations-related updates.

HPC Changelog

Changes to HPC systems are listed below, optionally filtered by system.

MVAPICH2 version 2.3 modules modified on Owens

Replace MV2_ENABLE_AFFINITY=0 with MV2_CPU_BINDING_POLICY=hybrid.

Known issues

Search Documentation

Search our client documentation below, optionally filtered by one or more systems.

Supercomputer: 

Supercomputers

We currently operate three major systems:

  • Owens Cluster, a 23,000+ core Dell Intel Xeon machine
  • Ruby Cluster, an 4800 core HP Intel Xeon machine
    • 20 nodes have Nvidia Tesla K40 GPUs
    • One node has 1 TB of RAM and 32 cores, for large SMP style jobs.
  • Pitzer Cluster, an 10,500+ core Dell Intel Xeon machine

Our clusters share a common environment, and we have several guides available.

OSC also provides more than 5 PB of storage, and another 5.5 PB of tape backup.

  • Learn how that space is made available to users, and how to best utilize the resources, in our storage environment guide.

Finally, you can keep up to date with any known issues on our systems (and the available workarounds). An archive of resolved issues can be found here.

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Owens

TIP: Remember to check the menu to the right of the page for related pages with more information about Owens' specifics.

OSC's Owens cluster being installed in 2016 is a Dell-built, Intel® Xeon® processor-based supercomputer.

Owens infographic,

Hardware

Owens_image

Detailed system specifications:

  • 824 Dell Nodes
  • Dense Compute
    • 648 compute nodes (Dell PowerEdge C6320 two-socket servers with Intel Xeon E5-2680 v4 (Broadwell, 14 cores, 2.40GHz) processors, 128GB memory)

  • GPU Compute

    • 1 60 ‘GPU ready’ compute nodes -- Dell PowerEdge R730 two-socket servers with Intel Xeon E5-2680 v4 (Broadwell, 14 cores, 2.40GHz) processors, 128GB memory

    • NVIDIA Tesla P100 (Pascal) GPUs -- 5.3TF peak (double precision), 16GB memory

  • Analytics

    • 16 huge memory nodes (Dell PowerEdge R930 four-socket server with Intel Xeon E5-4830 v3 (Haswell 12 core, 2.10GHz) processors, 1,536GB memory, 12 x 2TB drives)

  • 23,392 total cores
    • 28 cores/node  & 128GB of memory/node
  • Mellanox EDR (100Gbps) Infiniband networking
  • Theoretical system peak performance
    • ~750 teraflops (CPU only)
  • 4 login nodes:
    • Intel Xeon E5-2680 (Broadwell) CPUs
    • 28 cores/node and 256GB of memory/node

How to Connect

  • SSH Method

To login to Owens at OSC, ssh to the following hostname:

owens.osc.edu 

You can either use an ssh client application or execute ssh on the command line in a terminal window as follows:

ssh <username>@owens.osc.edu

You may see warning message including SSH key fingerprint. Verify that the fingerprint in the message matches one of the SSH key fingerprint listed here, then type yes.

From there, you are connected to Owens login node and have access to the compilers and other software development tools. You can run programs interactively or through batch requests. We use control groups on login nodes to keep the login nodes stable. Please use batch jobs for any compute-intensive or memory-intensive work. See the following sections for details.

  • OnDemand Method

You can also login to Owens at OSC with our OnDemand tool. The first step is to login to OnDemand. Then once logged in you can access Owens by clicking on "Clusters", and then selecting ">_Owens Shell Access".

Instructions on how to connect to OnDemand can be found at the OnDemand documention page.

File Systems

Owens accesses the same OSC mass storage environment as our other clusters. Therefore, users have the same home directory as on the old clusters. Full details of the storage environment are available in our storage environment guide.

Software Environment

The module system is used to manage the software environment on owens. Use  module load <package>  to add a software package to your environment. Use  module list  to see what modules are currently loaded and  module avail  to see the modules that are available to load. To search for modules that may not be visible due to dependencies or conflicts, use  module spider . By default, you will have the batch scheduling software modules, the Intel compiler and an appropriate version of mvapich2 loaded.

You can keep up to on the software packages that have been made available on Owens by viewing the Software by System page and selecting the Owens system.

Compiling Code to Use Advanced Vector Extensions (AVX2)

The Haswell and Broadwell processors that make up Owens support the Advanced Vector Extensions (AVX2) instruction set, but you must set the correct compiler flags to take advantage of it. AVX2 has the potential to speed up your code by a factor of 4 or more, depending on the compiler and options you would otherwise use.

In our experience, the Intel and PGI compilers do a much better job than the gnu compilers at optimizing HPC code.

With the Intel compilers, use -xHost and -O2 or higher. With the gnu compilers, use -march=native and -O3 . The PGI compilers by default use the highest available instruction set, so no additional flags are necessary.

This advice assumes that you are building and running your code on Owens. The executables will not be portable.  Of course, any highly optimized builds, such as those employing the options above, should be thoroughly validated for correctness.

See the Owens Programming Environment page for details.

Batch Specifics

Refer to the documentation for our batch environment to understand how to use the batch system on OSC hardware. Some specifics you will need to know to create well-formed batch scripts:

  • Most compute nodes on Owens have 28 cores/processors per node.  Huge-memory (analytics) nodes have 48 cores/processors per node.
  • Jobs on Owens may request partial nodes.
  • Owens has 8 debug nodes (6 regular nodes and 2 GPU nodes) which are specifically configured for short (< 1 hour) debugging type work.  These nodes have a time limit of 1 hour.

Using OSC Resources

For more information about how to use OSC resources, please see our guide on batch processing at OSC. For specific information about modules and file storage, please see the Batch Execution Environment page.

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Technical Specifications

The following are technical specifications for Owens.  

  Owens SYSTEM (2016)
NUMBER OF NODES 824 nodes
NUMBER OF CPU SOCKETS 1648 (2 sockets/node)
NUMBER OF CPU CORES 23,392 (28 cores/node)
CORES PER NODE 28 cores/node (48 cores/node for Huge Mem Nodes)
LOCAL DISK SPACE PER NODE

~1500GB in /tmp

COMPUTE CPU SPECIFICATIONS

Intel Xeon E5-2680 v4 (Broadwell) for compute

  • 2.4 GHz 
  • 14 cores per processor
COMPUTER SERVER SPECIFICATIONS

648 Dell PowerEdge C6320

160 Dell PowerEdge R730 (for accelerator nodes)

ACCELERATOR SPECIFICATIONS

NVIDIA P100 "Pascal" GPUs 16GB memory

NUMBER OF ACCELERATOR NODES

160 total

TOTAL MEMORY ~ 127 TB
MEMORY PER NODE

128 GB (1.5 TB for Huge Mem Nodes)

MEMORY PER CORE 4.5 GB (31 GB for Huge Mem)
INTERCONNECT  Mellanox EDR Infiniband Networking (100Gbps)
LOGIN SPECIFICATIONS

4 Intel Xeon E5-2680 (Broadwell) CPUs

  • 28 cores/node and 256GB of memory/node
SPECIAL NODES

16 Huge Memory Nodes

  • Dell PowerEdge R930 
  • 4 Intel Xeon E5-4830 v3 (Haswell)
    • 12 Cores
    • 2.1 GHz
  • 48 cores (12 cores/CPU)
  • 1.5 TB Memory
  • 12 x 2 TB Drive (20TB usable)

 

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Environment changes in Slurm migration

As we migrate to Slurm from Torque/Moab, there will be necessary software environment changes.

Decommissioning old MVAPICH2 versions

Old MVAPICH2 including mvapich2/2.1mvapich2/2.2 and its variants do not support Slurm very well due to its life span, so we will remove the following versions:

  • mvapich2/2.1
  • mvapich2/2.2, 2.2rc1, 2.2ddn1.3, 2.2ddn1.4, 2.2-debug, 2.2-gpu

As a result, the following dependent software will not be available anymore.

Unavailable Software Possible replacement
amber/16 amber/18
darshan/3.1.4 darshan/3.1.6
darshan/3.1.5-pre1 darshan/3.1.6
expresso/5.2.1 expresso/6.3
expresso/6.1 expresso/6.3
expresso/6.1.2 expresso/6.3
fftw3/3.3.4 fftw3/3.3.5
gamess/18Aug2016R1 gamess/30Sep2019R2
gromacs/2016.4 gromacs/2018.2
gromacs/5.1.2 gromacs/2018.2
lammps/14May16 lammps/16Mar18
lammps/31Mar17 lammps/16Mar18
mumps/5.0.2 N/A (no current users)
namd/2.11 namd/2.13
nwchem/6.6 nwchem/6.8
pnetcdf/1.7.0 pnetcdf/1.10.0
siesta-par/4.0 siesta-par/4.0.2

If you used one of the software listed above, we strongly recommend testing during the early user period. We listed a possible replacement version that is close to the unavailable version. However, if it is possible, we recommend using the most recent versions available. You can find the available versions by module spider {software name}. If you have any questions, please contact OSC Help.

Miscellaneous cleanup on MPIs

We clean up miscellaneous MPIs as we have a better and compatible version available. Since it has a compatible version, you should be able to use your applications without issues.

Removed MPI versions Compatible MPI versions

mvapich2/2.3b

mvapich2/2.3rc1

mvapich2/2.3rc2

mvapich2/2.3

mvapich2/2.3.3

mvapich2/2.3b-gpu

mvapich2/2.3rc1-gpu

mvapich2/2.3rc2-gpu

mvapich2/2.3-gpu

mvapich2/2.3.1-gpu

mvapich2-gdr/2.3.1, 2.3.2, 2.3.3

mvapich2-gdr/2.3.4

openmpi/1.10.5

openmpi/1.10

openmpi/1.10.7

openmpi/1.10.7-hpcx

openmpi/2.0

openmpi/2.0.3

openmpi/2.1.2

openmpi/2.1.6

openmpi/2.1.6-hpcx

openmpi/4.0.2

openmpi/4.0.2-hpcx

openmpi/4.0.3

openmpi/4.0.3-hpcx

Software flag usage update for Licensed Software

We have software flags required to use in job scripts for licensed software, such as ansys, abauqs, or schrodinger. With the slurm migration, we updated the syntax and added extra software flags.  It is very important everyone follow the procedure below. If you don't use the software flags properly, jobs submitted by others can be affected. 

We require using software flags only for the demanding software and the software features in order to prevent job failures due to insufficient licenses. When you use the software flags, Slurm will record it on its license pool, so that other jobs will launch when there are enough licenses available. This will function correctly when everyone uses the software flag.

During the early user period until Dec 15, 2020, the software flag system may not work correctly. This is because, during the test period, licenses will be used from two separate Owens systems. However, we recommend you to test your job scripts with the new software flags, so that you can use it without any issues after the slurm migration.

The new syntax for software flags is

#SBATCH -L {software flag}@osc:N

where N is the requesting number of the licenses. If you need more than one software flags, you can use

#SBATCH -L {software flag1}@osc:N,{software flag2}@osc:M

For example, if you need 2 abaqus and 2 abaqusextended license features, then you can use

$SBATCH -L abaqus@osc:2,abaqusextended@osc:2

We have the full list of software associated with software flags in the table below.

  Software flag Note
abaqus

abaqus, abaquscae,

abaqusexplicit, abaqusextended

 
ansys ansys, ansyspar  
comsol comsolscript  
schrodinger epik, glide, ligprep, macromodel, qikprep  
starccm starccm, starccmpar  
stata stata  
usearch usearch  
 
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Owens Programming Environment (PBS)

This document is obsoleted and kept as a reference to previous Owens programming environment. Please refer to here for the latest version.

Compilers

C, C++ and Fortran are supported on the Owens cluster. Intel, PGI and GNU compiler suites are available. The Intel development tool chain is loaded by default. Compiler commands and recommended options for serial programs are listed in the table below. See also our compilation guide.

The Haswell and Broadwell processors that make up Owens support the Advanced Vector Extensions (AVX2) instruction set, but you must set the correct compiler flags to take advantage of it. AVX2 has the potential to speed up your code by a factor of 4 or more, depending on the compiler and options you would otherwise use.

In our experience, the Intel and PGI compilers do a much better job than the GNU compilers at optimizing HPC code.

With the Intel compilers, use -xHost and -O2 or higher. With the GNU compilers, use -march=native and -O3. The PGI compilers by default use the highest available instruction set, so no additional flags are necessary.

This advice assumes that you are building and running your code on Owens. The executables will not be portable.  Of course, any highly optimized builds, such as those employing the options above, should be thoroughly validated for correctness.

LANGUAGE INTEL EXAMPLE PGI EXAMPLE GNU EXAMPLE
C icc -O2 -xHost hello.c pgcc -fast hello.c gcc -O3 -march=native hello.c
Fortran 90 ifort -O2 -xHost hello.f90 pgf90 -fast hello.f90 gfortran -O3 -march=native hello.f90
C++ icpc -O2 -xHost hello.cpp pgc++ -fast hello.cpp g++ -O3 -march=native hello.cpp

Parallel Programming

MPI

OSC systems use the MVAPICH2 implementation of the Message Passing Interface (MPI), optimized for the high-speed Infiniband interconnect. MPI is a standard library for performing parallel processing using a distributed-memory model. For more information on building your MPI codes, please visit the MPI Library documentation.

Parallel programs are started with the mpiexec command. For example,

mpiexec ./myprog

The program to be run must either be in your path or have its path specified.

The mpiexec command will normally spawn one MPI process per CPU core requested in a batch job. Use the -n and/or -ppn option to change that behavior.

The table below shows some commonly used options. Use mpiexec -help for more information.

MPIEXEC Option COMMENT
-ppn 1 One process per node
-ppn procs procs processes per node
-n totalprocs
-np totalprocs
At most totalprocs processes per node
-prepend-rank Prepend rank to output
-help Get a list of available options

 

Caution: There are many variations on mpiexec and mpiexec.hydra. Information found on non-OSC websites may not be applicable to our installation.
The information above applies to the MVAPICH2 and IntelMPI installations at OSC. See the OpenMPI software page for mpiexec usage with OpenMPI.

OpenMP

The Intel, PGI and GNU compilers understand the OpenMP set of directives, which support multithreaded programming. For more information on building OpenMP codes on OSC systems, please visit the OpenMP documentation.

GPU Programming

160 Nvidia P100 GPUs are available on Owens.  Please visit our GPU documentation.

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Owens Programming Environment

Compilers

C, C++ and Fortran are supported on the Owens cluster. Intel, PGI and GNU compiler suites are available. The Intel development tool chain is loaded by default. Compiler commands and recommended options for serial programs are listed in the table below. See also our compilation guide.

The Haswell and Broadwell processors that make up Owens support the Advanced Vector Extensions (AVX2) instruction set, but you must set the correct compiler flags to take advantage of it. AVX2 has the potential to speed up your code by a factor of 4 or more, depending on the compiler and options you would otherwise use.

In our experience, the Intel and PGI compilers do a much better job than the GNU compilers at optimizing HPC code.

With the Intel compilers, use -xHost and -O2 or higher. With the GNU compilers, use -march=native and -O3. The PGI compilers by default use the highest available instruction set, so no additional flags are necessary.

This advice assumes that you are building and running your code on Owens. The executables will not be portable.  Of course, any highly optimized builds, such as those employing the options above, should be thoroughly validated for correctness.

LANGUAGE INTEL GNU PGI
C icc -O2 -xHost hello.c gcc -O3 -march=native hello.c pgcc -fast hello.c
Fortran 77/90 ifort -O2 -xHost hello.F gfortran -O3 -march=native hello.F pgfortran -fast hello.F
C++ icpc -O2 -xHost hello.cpp g++ -O3 -march=native hello.cpp pgc++ -fast hello.cpp

Parallel Programming

MPI

OSC systems use the MVAPICH2 implementation of the Message Passing Interface (MPI), optimized for the high-speed Infiniband interconnect. MPI is a standard library for performing parallel processing using a distributed-memory model. For more information on building your MPI codes, please visit the MPI Library documentation.

MPI programs are started with the srun command. For example,

#!/bin/bash
#SBATCH --nodes=2

srun [ options ] mpi_prog
Note: the program to be run must either be in your path or have its path specified.

The srun command will normally spawn one MPI process per task requested in a Slurm batch job. Use the -n ntasks and/or --ntasks-per-node=n option to change that behavior. For example,

#!/bin/bash
#SBATCH --nodes=2

# Use the maximum number of CPUs of two nodes
srun ./mpi_prog

# Run 8 processes per node
srun --ntasks-per-node=8  ./mpi_prog

The table below shows some commonly used options. Use srun -help for more information.

OPTION COMMENT
-n, --ntasks=ntasks total number of tasks to run
--ntasks-per-node=n number of tasks to invoke on each node
-help Get a list of available options
Note: The information above applies to the MVAPICH2, Intel MPI and OpenMPI installations at OSC. 
Caution: mpiexec or mpiexec.hydra is still supported with Intel MPI and OpenMPI. Please refer to the Intel MPI and OpenMPI software pages for more detail.

OpenMP

The Intel, GNU and PGI compilers understand the OpenMP set of directives, which support multithreaded programming. For more information on building OpenMP codes on OSC systems, please visit the OpenMP documentation.

An OpenMP program by default will use a number of threads equal to the number of CPUs requested in a Slurm batch job. To use a different number of threads, set the environment variable OMP_NUM_THREADS. For example,

#!/bin/bash
#SBATCH --ntask=8

# Run 8 threads
./omp_prog

# Run 4 threads
export OMP_NUM_THREADS=4
./omp_prog

To run a OpenMP job on an exclusive node:

#!/bin/bash
#SBATCH --nodes=1
#SBATCH --exclusive

export OMP_NUM_THREADS=$SLURM_CPUS_ON_NODE
./omp_prog

Interactive job only

Please use -c, --cpus-per-task=X instead of -n, --ntasks=X to request an interactive job. Both result in an interactive job with X CPUs available but only the former option automatically assigns the correct number of threads to the OpenMP program. If  the option --ntasks is used only, the OpenMP program will use one thread or all threads will be bound to one CPU core. 

Hybrid (MPI + OpenMP)

An example of running a job for hybrid code:

#!/bin/bash
#SBATCH --nodes=2
#SBATCH --tasks-per-node=4
#SBATCH --cpus-per-task=7

# Run 4 MPI processes on each node and 7 OpenMP threads spawned from a MPI process
export OMP_NUM_THREADS=7
srun ./hybrid_prog

 

Tuning Parallel Program Performance: Process/Thread Placement

To get the maximum performance, it is important to make sure that processes/threads are located as close as possible to their data, and as close as possible to each other if they need to work on the same piece of data, with given the arrangement of node, sockets, and cores, with different access to RAM and caches. 

While cache and memory contention between threads/processes are an issue, it is best to use scatter distribution for code. 

Processes and threads are placed differently depending on the computing resources you requste and the compiler and MPI implementation used to compile your code. For the former, see the above examples to learn how to run a job on exclusive nodes. For the latter, this section summarizes the default behavior and how to modify placement.

OpenMP only

For all three compilers (Intel, GNU, PGI), purely threaded codes do not bind to particular CPU cores by default. In other words, it is possible that multiple threads are bound to the same CPU core

The following table describes how to modify the default placements for pure threaded code:

DISTRIBUTION Compact Scatter/Cyclic
DESCRIPTION Place threads as closely as possible on sockets Distribute threads as evenly as possible across sockets
INTEL KMP_AFFINITY=compact KMP_AFFINITY=scatter
GNU OMP_PLACES=sockets[1] OMP_PROC_BIND=spread/close
PGI[2]

MP_BIND=yes
MP_BLIST="$(seq -s, 0 2 27),$(seq -s, 1 2 27)" 

MP_BIND=yes
  1. Threads in the same socket might be bound to the same CPU core.
  2. PGI LLVM-backend (version 19.1 and later) does not support thread/processors affinity on NUMA architecture. To enable this feature, compile threaded code with --Mnollvm to use proprietary backend.

MPI Only

For MPI-only codes, MVAPICH2 first binds as many processes as possible on one socket, then allocates the remaining processes on the second socket so that consecutive tasks are near each other.  Intel MPI and OpenMPI alternately bind processes on socket 1, socket 2, socket 1, socket 2 etc, as cyclic distribution.

For process distribution across nodes, all MPIs first bind as many processes as possible on one node, then allocates the remaining processes on the second node. 

The following table describe how to modify the default placements on a single node for MPI-only code with the command srun:

DISTRIBUTION
(single node)
Compact Scatter/Cyclic
DESCRIPTION Place processs as closely as possible on sockets Distribute process as evenly as possible across sockets
MVAPICH2[1] Default MV2_CPU_BINDING_POLICY=scatter
MVAPICH2
(2.3.4 &  later)
srun --cpu-bind="map_cpu:$(seq -s, 0 2 27),$(seq -s, 1 2 27)" Default
INTEL MPI srun --cpu-bind="map_cpu:$(seq -s, 0 2 27),$(seq -s, 1 2 27)" Default
OPENMPI srun --cpu-bind="map_cpu:$(seq -s, 0 2 27),$(seq -s, 1 2 27)" Default
  1. MV2_CPU_BINDING_POLICY will not work if MV2_ENABLE_AFFINITY=0 is set.

To distribute processes evenly across nodes, please set SLURM_DISTRIBUTION=cyclic.

Hybrid (MPI + OpenMP)

For Hybrid codes, each MPI process is allocated  OMP_NUM_THREADS cores and the threads of each process are bound to those cores. All MPI processes (as well as the threads bound to the process) behave as we describe in the previous sections. It means the threads spawned from a MPI process might be bound to the same core. To change the default process/thread placmements, please refer to the tables above. 

Summary

The above tables list the most commonly used settings for process/thread placement. Some compilers and Intel libraries may have additional options for process and thread placement beyond those mentioned on this page. For more information on a specific compiler/library, check the more detailed documentation for that library.

GPU Programming

160 Nvidia P100 GPUs are available on Owens.  Please visit our GPU documentation.

Reference

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Queues and Reservations

Here are the queues available on Owens. Please note that you will be routed to the appropriate queue based on your walltime and job size request.

Name Nodes available max walltime max job size notes

Serial

Available minus reservations

168 hours

1 node

 

Parallel

Available minus reservations

 96 hours

8 nodes

 

Largeparallel

Available minus reservations

96 hours

81 nodes

 

Hugemem

16

96 hours

1 node

 
Parhugemem 16 96 hours 16

Restricted access. 

Use "-q parhugemem" to request it

Debug

6 regular nodes

4 GPU nodes

1 hour 2 nodes

For small interactive and test jobs during 8AM-6PM, Monday - Friday. 

Use "-q debug" to request it 

"Available minus reservations" means all nodes in the cluster currently operational (this will fluctuate slightly), less the reservations listed below. To access one of the restricted queues, please contact OSC Help. Generally, access will only be granted to these queues if the performance of the job cannot be improved, and job size cannot be reduced by splitting or checkpointing the job.

 

Occasionally, reservations will be created for specific projects that will not be reflected in these tables.

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Citation

For more information about citations of OSC, visit https://www.osc.edu/citation.

To cite Owens, please use the following Archival Resource Key:

ark:/19495/hpc6h5b1

Please adjust this citation to fit the citation style guidelines required.

Ohio Supercomputer Center. 2016. Owens Supercomputer. Columbus, OH: Ohio Supercomputer Center. http://osc.edu/ark:19495/hpc6h5b1

Here is the citation in BibTeX format:

@misc{Owens2016,
ark = {ark:/19495/hpc93fc8},
url = {http://osc.edu/ark:/19495/hpc6h5b1},
year  = {2016},
author = {Ohio Supercomputer Center},
title = {Owens Supercomputer}
}

And in EndNote format:

%0 Generic
%T Owens Supercomputer
%A Ohio Supercomputer Center
%R ark:/19495/hpc6h5b1
%U http://osc.edu/ark:/19495/hpc6h5b1
%D 2016

Here is an .ris file to better suit your needs. Please change the import option to .ris.

Documentation Attachment: 
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Owens SSH key fingerprints

These are the public key fingerprints for Owens:
owens: ssh_host_rsa_key.pub = 18:68:d4:b0:44:a8:e2:74:59:cc:c8:e3:3a:fa:a5:3f
owens: ssh_host_ed25519_key.pub = 1c:3d:f9:99:79:06:ac:6e:3a:4b:26:81:69:1a:ce:83
owens: ssh_host_ecdsa_key.pub = d6:92:d1:b0:eb:bc:18:86:0c:df:c5:48:29:71:24:af


These are the SHA256 hashes:​
owens: ssh_host_rsa_key.pub = SHA256:vYIOstM2e8xp7WDy5Dua1pt/FxmMJEsHtubqEowOaxo
owens: ssh_host_ed25519_key.pub = SHA256:FSb9ZxUoj5biXhAX85tcJ/+OmTnyFenaSy5ynkRIgV8
owens: ssh_host_ecdsa_key.pub = SHA256:+fqAIqaMW/DUJDB0v/FTxMT9rkbvi/qVdMKVROHmAP4

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Batch Limit Rules

Memory Limit:

It is strongly suggested to consider the available per-core memory when users request OSC resources for their jobs.

Regular Dense Compute Node

On Owens, it equates to 4315MB/core or 118GB/node for the regular dense compute node. 

If your job requests less than a full node ( ppn< 28 ), it may be scheduled on a node with other running jobs. In this case, your job is entitled to a memory allocation proportional to the number of cores requested (4315MB/core).  For example, without any memory request ( mem=XX ), a job that requests  nodes=1:ppn=1  will be assigned one core and should use no more than 4315MB of RAM, a job that requests  nodes=1:ppn=3  will be assigned 3 cores and should use no more than 3*4315MB of RAM, and a job that requests  nodes=1:ppn=28  will be assigned the whole node (28 cores) with 118GB of RAM.  

Here is some information when you include memory request (mem=XX ) in your job. A job that requests  nodes=1:ppn=1,mem=12GB  will be assigned one core and have access to 12GB of RAM, and charged for 3 cores worth of usage.  However, a job that requests  nodes=1:ppn=5,mem=12GB  will be assigned 5 cores but have access to only 12GB of RAM, and charged for 5 cores worth of usage. 

A multi-node job ( nodes>1 ) will be assigned the entire nodes with 118 GB/node and charged for the entire nodes regardless of ppn request. For example, a job that requests  nodes=10:ppn=1 will be charged for 10 whole nodes (28 cores/node*10 nodes, which is 280 cores worth of usage).  

Huge Memory Node

Beginning on Tuesday, March 10th, 2020, users are able to run jobs using less than a full huge memory node. Please read the following instructions carefully before requesting a huge memory node on Owens. 

On Owens, it has 1,493GB/node with 48 cores for a huge memory node.

Please always specify a memory limit in your job request if your job requests less than a full node ( ppn< 48 ) ; otherwise, we will allocate 4315MB/core only for your job. For example, use nodes=1:ppn=30, mem=960GB  will be assigned 30 cores and 960 GB of RAM of a huge memory node. However, without any memory request ( mem=XX ), a job that requests  nodes=1:ppn=30  will be assigned 30 cores of a huge memory node and should use no more than 4315MB*30 of RAM; while a job that requests  nodes=1:ppn=1, mem=960GB  will be assigned 1 core of a huge memory node and should use no more than 960 GB of RAM. 

A job that requests huge-memory node ( nodes=1:ppn=48  ) will be allocated the entire huge-memory node with 1493GB of RAM and charged for the whole node (48 cores worth of usage).

To manage and monitor your memory usage, please refer to Out-of-Memory (OOM) or Excessive Memory Usage.

Walltime Limit

Here are the queues available on Owens:

NAME

MAX WALLTIME

MAX JOB SIZE

NOTES

Serial

 168 hours

1 node

 

longserial 336 hours 1 node
  • Restricted access (contact OSC Help if you need access)

Parallel

96 hours

81 nodes

 

Hugemem

168 hours

1 node

16 nodes in this class
Parallel hugemem 96 hours 16 nodes
  • Restricted access (contact OSC Help if you need access)
  • Use "-q parhugemem" to access it

Debug

1 hour

2 nodes

  • Use "-q debug" to request it 

GPU Jobs

There is only one GPU per GPU node on Owens.

For serial jobs, we allow node sharing on GPU nodes so a job may request any number of cores (up to 28)

(nodes=1:ppn=XX:gpus=1)

For parallel jobs (n>1), we do not allow node sharing.

Job/Core Limits

  Max Running Job Limit Soft Max Core/Processor Limit Hard Max Core/Processor Limt
Individual User 384 3080 3080
Project/Group 576 3080 4620

The soft and hard max limits above apply depending on different system resource availability. If resources are scarce, then the soft max limit is used to increase the fairness of allocating resources. Otherwise, if there are idle resources, then the hard max limit is used to increase system utilization.

An individual user can have up to the max concurrently running jobs and/or up to the max processors/cores in use.

However, among all the users in a particular group/project, they can have up to the max concurrently running jobs and/or up to the max processors/cores in use.

A user may have no more than 1000 jobs submitted to both the parallel and serial job queue separately.
Supercomputer: 
Service: 

Pitzer

TIP: Remember to check the menu to the right of the page for related pages with more information about Pitzer's specifics.

OSC's original Pitzer cluster was installed in late 2018 and is a Dell-built, Intel® Xeon® 'Skylake' processor-based supercomputer with 260 nodes.

In September 2020, OSC installed additional 398 Intel® Xeon® 'Cascade Lake' processor-based nodes as part of a Pitzer Expansion cluster. 

pitzer-new.jpg

Hardware

Photo of Pitzer Cluster

Detailed system specifications:

  Deployed in 2018 Deployed in 2020 Total
Total Compute Nodes 260 Dell nodes 398 Dell nodes 658 Dell nodes
Total CPU Cores 10,560 total cores 19,104 total cores 29,664 total cores
Standard Dense Compute Nodes

224 nodes​​​​​​

  • Dual Intel Xeon 6148s Skylakes
  • 40 cores per node @ 2.4GHz
  • 192GB memory
  • 1 TB disk space
340 nodes
  • Dual Intel Xeon 8268s Cascade Lakes
  • 48 cores per node @ 2.9GHz
  • 192GB memory 
  • 1 TB disk space
564 nodes
Dual GPU Compute Nodes 32 nodes
  • Dual Intel Xeon 6148s
  • Dual NVIDIA Volta V100 w/ 16GB GPU memory
  • 40 cores per node @ 2.4GHz
  • 384GB memory
  • 1 TB disk space
42 nodes
  • Dual Intel Xeon 8268s 
  • Dual NVIDIA Volta V100 w/32GB GPU memory
  • 48 cores per node @ 2.9GHz
  • 384GB memory
  • 1 TB disk space
74 dual GPU nodes
Quad GPU Compute Nodes N/A 4 nodes 
  • Dual Intel Xeon 8260s Cascade Lakes
  • Quad NVIDIA Volta V100s w/32GB GPU memory and NVLink
  • 48 cores per node @ 2.4GHz
  • 768GB memory
  • 4 TB disk space
4 quad GPU nodes
Large Memory Compute Nodes 4 nodes
  • Quad Processor Intel Xeon 6148 Skylakes
  • 80 cores per node @ 2.4GHz
  • 3TB memory
  • 1 TB disk space
12 nodes
  • Dual Intel Xeon 8268 Cascade Lakes
  • 48 cores per node @ 2.9GHz
  • 768GB memory
  • 0.5 TB disk space
16 nodes
Interactive Login Nodes

4 nodes

  • Dual Intel Xeon 6148s
  • 368GB memory
4 nodes
InfiniBand High-Speed Network Mellanox EDR (100Gbps) Infiniband networking Mellanox EDR (100Gbps) Infiniband networking  
Theoretical Peak Performance

~850 TFLOPS (CPU only)

~450 TFLOPS (GPU only)

~1300 TFLOPS (total)

~3090 TFLOPS (CPU only)

~710 TFLOPS (GPU only)

~3800 TFLOPS (total)

~3940TFLOPS (CPU only)

~1160 TFLOPS (GPU only)

~5100 TFLOPS (total)

How to Connect

  • SSH Method

To login to Pitzer at OSC, ssh to the following hostname:

pitzer.osc.edu 

You can either use an ssh client application or execute ssh on the command line in a terminal window as follows:

ssh <username>@pitzer.osc.edu

You may see a warning message including SSH key fingerprint. Verify that the fingerprint in the message matches one of the SSH key fingerprints listed here, then type yes.

From there, you are connected to the Pitzer login node and have access to the compilers and other software development tools. You can run programs interactively or through batch requests. We use control groups on login nodes to keep the login nodes stable. Please use batch jobs for any compute-intensive or memory-intensive work. See the following sections for details.

  • OnDemand Method

You can also login to Pitzer at OSC with our OnDemand tool. The first step is to log into OnDemand. Then once logged in you can access Pitzer by clicking on "Clusters", and then selecting ">_Pitzer Shell Access".

Instructions on how to connect to OnDemand can be found at the OnDemand documentation page.

File Systems

Pitzer accesses the same OSC mass storage environment as our other clusters. Therefore, users have the same home directory as on the old clusters. Full details of the storage environment are available in our storage environment guide.

Software Environment

The module system on Pitzer is the same as on the Owens and Ruby systems. Use  module load <package>  to add a software package to your environment. Use  module list  to see what modules are currently loaded and  module avail  to see the modules that are available to load. To search for modules that may not be visible due to dependencies or conflicts, use  module spider . By default, you will have the batch scheduling software modules, the Intel compiler, and an appropriate version of mvapich2 loaded.

You can keep up to the software packages that have been made available on Pitzer by viewing the Software by System page and selecting the Pitzer system.

Compiling Code to Use Advanced Vector Extensions (AVX2)

The Skylake processors that make Pitzer support the Advanced Vector Extensions (AVX2) instruction set, but you must set the correct compiler flags to take advantage of it. AVX2 has the potential to speed up your code by a factor of 4 or more, depending on the compiler and options you would otherwise use.

In our experience, the Intel and PGI compilers do a much better job than the gnu compilers at optimizing HPC code.

With the Intel compilers, use -xHost and -O2 or higher. With the gnu compilers, use -march=native and -O3 . The PGI compilers by default use the highest available instruction set, so no additional flags are necessary.

This advice assumes that you are building and running your code on Pitzer. The executables will not be portable.  Of course, any highly optimized builds, such as those employing the options above, should be thoroughly validated for correctness.

See the Pitzer Programming Environment page for details.

Batch Specifics

On September 22, 2020, OSC switches to Slurm for job scheduling and resource management on the Pitzer Cluster.

Refer to this Slurm migration page to understand how to use Slurm on the Pitzer cluster. Some specifics you will need to know to create well-formed batch scripts:

  • OSC enables PBS compatibility layer provided by Slurm such that PBS batch scripts that used to work in the previous Torque/Moab environment mostly still work in Slurm. 
  • Pitzer is a heterogeneous system with mixed types of CPUs after the expansion as shown in the above table. Please be cautious when requesting resources on Pitzer and check this page for more detailed discussions
  • Jobs on Pitzer may request partial nodes.  

Using OSC Resources

For more information about how to use OSC resources, please see our guide on batch processing at OSC and Slurm migration. For specific information about modules and file storage, please see the Batch Execution Environment page.

Technical Specifications

The following are technical specifications for Pitzer.  

  Pitzer SYSTEM (2018) Pitzer SYSTEM (2020)
NUMBER OF NODES 260 nodes 398 nodes
NUMBER OF CPU SOCKETS 528 (2 sockets/node for standard node) 796 (2 sockets/node for all nodes)
NUMBER OF CPU CORES 10,560 (40 cores/node for standard node) 19,104 (48 cores/node for all nodes)
CORES PER NODE 40 cores/node (80 cores/node for Huge Mem Nodes) 48 cores/node for all nodes
LOCAL DISK SPACE PER NODE

850 GB in /tmp

1 TB for most nodes

4 TB for quad GPU

0.5 TB for large mem

 

COMPUTE CPU SPECIFICATIONS

Intel Xeon Gold 6148 (Skylake) for compute

  • 2.4 GHz 
  • 20 cores per processor

Intel Xeon 8268s Cascade Lakes for most compute

  • 2.9 GHz
  • 24 cores per processor
COMPUTER SERVER SPECIFICATIONS

224 Dell PowerEdge C6420

32 Dell PowerEdge R740 (for accelerator nodes)

4 Dell PowerEdge R940

352 Dell PowerEdge C6420

42 Dell PowerEdge R740 (for dual GPU nodes)

4 Dell Poweredge c4140 (for quad GPU nodes)

 

ACCELERATOR SPECIFICATIONS

NVIDIA V100 "Volta" GPUs 16GB memory

NVIDIA V100 "Volta" GPUs 32GB memory for dual GPU

NVIDIA V100 "Volta" GPUs 32GB memory and NVLink for quad GPU

NUMBER OF ACCELERATOR NODES

32 total (2 GPUs per node)

42 dual GPU nodes (2 GPUs per node)

4 quad GPU nodes (4 GPUs per node)

TOTAL MEMORY ~ 67 TB ~ 95 TB
MEMORY PER NODE

192 GB for standard nodes

384 GB for accelerator nodes

3 TB for Huge Mem Nodes

192 GB for standard nodes

384 GB for dual GPU nodes

768 GB for quad and Large Mem Nodes

MEMORY PER CORE

4.8 GB for standard nodes

9.6 GB for accelerator nodes

76.8 GB for Huge Mem

4.0 GB for standard nodes

8.0 GB for dual GPU nodes

16.0 GB for quad and Large Mem Nodes

INTERCONNECT  Mellanox EDR Infiniband Networking (100Gbps) Mellanox EDR Infiniband Networking (100Gbps)
LOGIN SPECIFICATIONS

4 Intel Xeon Gold 6148 (Skylake) CPUs

  • 40 cores/node and 384 GB of memory/node
SPECIAL NODES

4 Huge Memory Nodes

  • Dell PowerEdge R940 
  • 4 Intel Xeon Gold 6148 (Skylake)
    • 20 Cores
    • 2.4 GHz
  • 80 cores (20 cores/CPU)
  • 3 TB Memory
  • 2x Mirror 1 TB Drive (1 TB usable)
4 quad GPU Nodes 
  • Dual Intel Xeon 8260s Cascade Lakes
  • Quad NVIDIA Volta V100s w/32GB GPU memory and NVLink
  • 48 cores per node @ 2.4GHz
  • 768GB memory
  • 4 TB disk space

12 Large Memory Nodes

  • Dual Intel Xeon 8268 Cascade Lakes
  • 48 cores per node @ 2.9GHz
  • 768GB memory
  • 0.5 TB disk space
Supercomputer: 

Pitzer Programming Environment (PBS)

This document is obsoleted and kept as a reference to previous Pitzer programming environment. Please refer to here for the latest version.

Compilers

C, C++ and Fortran are supported on the Pitzer cluster. Intel, PGI and GNU compiler suites are available. The Intel development tool chain is loaded by default. Compiler commands and recommended options for serial programs are listed in the table below. See also our compilation guide.

The Skylake processors that make up Pitzer support the Advanced Vector Extensions (AVX512) instruction set, but you must set the correct compiler flags to take advantage of it. AVX512 has the potential to speed up your code by a factor of 8 or more, depending on the compiler and options you would otherwise use. However, bare in mind that clock speeds decrease as the level of the instruction set increases. So, if your code does not benefit from vectorization it may be beneficial to use a lower instruction set.

In our experience, the Intel and PGI compilers do a much better job than the GNU compilers at optimizing HPC code.

With the Intel compilers, use -xHost and -O2 or higher. With the GNU compilers, use -march=native and -O3. The PGI compilers by default use the highest available instruction set, so no additional flags are necessary.

This advice assumes that you are building and running your code on Owens. The executables will not be portable.  Of course, any highly optimized builds, such as those employing the options above, should be thoroughly validated for correctness.

LANGUAGE INTEL EXAMPLE PGI EXAMPLE GNU EXAMPLE
C icc -O2 -xHost hello.c pgcc -fast hello.c gcc -O3 -march=native hello.c
Fortran 90 ifort -O2 -xHost hello.f90 pgf90 -fast hello.f90 gfortran -O3 -march=native hello.f90
C++ icpc -O2 -xHost hello.cpp pgc++ -fast hello.cpp g++ -O3 -march=native hello.cpp

Parallel Programming

MPI

OSC systems use the MVAPICH2 implementation of the Message Passing Interface (MPI), optimized for the high-speed Infiniband interconnect. MPI is a standard library for performing parallel processing using a distributed-memory model. For more information on building your MPI codes, please visit the MPI Library documentation.

Parallel programs are started with the mpiexec command. For example,

mpiexec ./myprog

The program to be run must either be in your path or have its path specified.

The mpiexec command will normally spawn one MPI process per CPU core requested in a batch job. Use the -n and/or -ppn option to change that behavior.

The table below shows some commonly used options. Use mpiexec -help for more information.

MPIEXEC OPTION COMMENT
-ppn 1 One process per node
-ppn procs procs processes per node
-n totalprocs
-np totalprocs
At most totalprocs processes per node
-prepend-rank Prepend rank to output
-help Get a list of available options

 

Caution: There are many variations on mpiexec and mpiexec.hydra. Information found on non-OSC websites may not be applicable to our installation.
The information above applies to the MVAPICH2 and IntelMPI installations at OSC. See the OpenMPI software page for mpiexec usage with OpenMPI.

OpenMP

The Intel, PGI and GNU compilers understand the OpenMP set of directives, which support multithreaded programming. For more information on building OpenMP codes on OSC systems, please visit the OpenMP documentation.

 

Process/Thread placement

Processes and threads are placed differently depending on the compiler and MPI implementation used to compile your code. This section summarizes the default behavior and how to modify placement.

For all three compilers (Intel, GNU, PGI), purely threaded codes do not bind to particular cores by default.

For MPI-only codes, Intel MPI first binds the first half of processes to one socket, and then second half to the second socket so that consecutive tasks are located near each other. MVAPICH2 first binds as many processes as possible on one socket, then allocates the remaining processes on the second socket so that consecutive tasks are near each other. OpenMPI alternately binds processes on socket 1, socket 2, socket 1, socket 2, etc, with no particular order for the core id.

For Hybrid codes, Intel MPI first binds the first half of processes to one socket, and then second half to the second socket so that consecutive tasks are located near each other. Each process is allocated ${OMP_NUM_THREADS} cores and the threads of each process are bound to those cores. MVAPICH2 allocates ${OMP_NUM_THREADS} cores for each process and each thread of a process is placed on a separate core. By default, OpenMPI  behaves the same for hybrid codes as it does for MPI-only codes, allocating a single core for each process and all threads of that process.

The following tables describe how to modify the default placements for each type of code.

OpenMP options:

Option Intel GNU Pgi description
Scatter KMP_AFFINITY=scatter OMP_PLACES=cores OMP_PROC_BIND=close/spread MP_BIND=yes Distribute threads as evenly as possible across system
Compact KMP_AFFINITY=compact OMP_PLACES=sockets MP_BIND=yes MP_BLIST="0,2,4,6,8,10,1,3,5,7,9" Place threads as closely as possible on system

 

MPI options:

OPTION INTEL MVAPICh2 openmpi DESCRIPTION
Scatter I_MPI_PIN_DOMAIN=core I_MPI_PIN_ORDER=scatter MV2_CPU_BINDING_POLICY=scatter -map-by core --rank-by socket:span Distribute processes as evenly as possible across system
Compact I_MPI_PIN_DOMAIN=core I_MPI_PIN_ORDER=compact MV2_CPU_BINDING_POLICY=bunch -map-by core

Distribute processes as closely as possible on system

 

Hybrid MPI+OpenMP options (combine with options from OpenMP table for thread affinity within cores allocated to each process):

OPTION INTEL MVAPICH2 OPENMPI DESCRIPTION
Scatter I_MPI_PIN_DOMAIN=omp I_MPI_PIN_ORDER=scatter MV2_CPU_BINDING_POLICY=hybrid MV2_HYBRID_BINDING_POLICY=linear -map-by node:PE=$OMP_NUM_THREADS --bind-to core --rank-by socket:span Distrubute processes as evenly as possible across system ($OMP_NUM_THREADS cores per process)
Compact I_MPI_PIN_DOMAIN=omp I_MPI_PIN_ORDER=compact MV2_CPU_BINDING_POLICY=hybrid MV2_HYBRID_BINDING_POLICY=spread -map-by node:PE=$OMP_NUM_THREADS --bind-to core Distribute processes as closely as possible on system ($OMP_NUM_THREADS cores per process)

 

 

The above tables list the most commonly used settings for process/thread placement. Some compilers and Intel libraries may have additional options for process and thread placement beyond those mentioned on this page. For more information on a specific compiler/library, check the more detailed documentation for that library.

GPU Programming

64 Nvidia V100 GPUs are available on Pitzer.  Please visit our GPU documentation.

 
 
 
Supercomputer: 

Pitzer Programming Environment

Compilers

C, C++ and Fortran are supported on the Pitzer cluster. Intel, PGI and GNU compiler suites are available. The Intel development tool chain is loaded by default. Compiler commands and recommended options for serial programs are listed in the table below. See also our compilation guide.

The Skylake and Cascade Lake processors that make up Pitzer support the Advanced Vector Extensions (AVX512) instruction set, but you must set the correct compiler flags to take advantage of it. AVX512 has the potential to speed up your code by a factor of 8 or more, depending on the compiler and options you would otherwise use. However, bare in mind that clock speeds decrease as the level of the instruction set increases. So, if your code does not benefit from vectorization it may be beneficial to use a lower instruction set.

In our experience, the Intel compiler usually does the best job of optimizing numerical codes and we recommend that you give it a try if you’ve been using another compiler.

With the Intel compilers, use -xHost and -O2 or higher. With the GNU compilers, use -march=native and -O3. The PGI compilers by default use the highest available instruction set, so no additional flags are necessary.

This advice assumes that you are building and running your code on Owens. The executables will not be portable.  Of course, any highly optimized builds, such as those employing the options above, should be thoroughly validated for correctness.

LANGUAGE INTEL GNU PGI
C icc -O2 -xHost hello.c gcc -O3 -march=native hello.c pgcc -fast hello.c
Fortran 77/90 ifort -O2 -xHost hello.F gfortran -O3 -march=native hello.F pgfortran -fast hello.F
C++ icpc -O2 -xHost hello.cpp g++ -O3 -march=native hello.cpp pgc++ -fast hello.cpp

Parallel Programming

MPI

OSC systems use the MVAPICH2 implementation of the Message Passing Interface (MPI), optimized for the high-speed Infiniband interconnect. MPI is a standard library for performing parallel processing using a distributed-memory model. For more information on building your MPI codes, please visit the MPI Library documentation.

MPI programs are started with the srun command. For example,

#!/bin/bash
#SBATCH --nodes=2

srun [ options ] mpi_prog
Note: the program to be run must either be in your path or have its path specified.

The srun command will normally spawn one MPI process per task requested in a Slurm batch job. Use the -n ntasks and/or --ntasks-per-node=n option to change that behavior. For example,

#!/bin/bash
#SBATCH --nodes=2

# Use the maximum number of CPUs of two nodes
srun ./mpi_prog

# Run 8 processes per node
srun --ntasks-per-node=8  ./mpi_prog

The table below shows some commonly used options. Use srun -help for more information.

OPTION COMMENT
-n, --ntasks=ntasks total number of tasks to run
--ntasks-per-node=n number of tasks to invoke on each node
-help Get a list of available options
Note: The information above applies to the MVAPICH2, Intel MPI and OpenMPI installations at OSC. 
Caution: mpiexec or mpiexec.hydra is still supported with Intel MPI and OpenMPI. Please refer to the Intel MPI and OpenMPI software pages for more detail.

OpenMP

The Intel, GNU and PGI compilers understand the OpenMP set of directives, which support multithreaded programming. For more information on building OpenMP codes on OSC systems, please visit the OpenMP documentation.

An OpenMP program by default will use a number of threads equal to the number of CPUs requested in a Slurm batch job. To use a different number of threads, set the environment variable OMP_NUM_THREADS. For example,

#!/bin/bash
#SBATCH --ntask=8

# Run 8 threads
./omp_prog

# Run 4 threads
export OMP_NUM_THREADS=4
./omp_prog

To run a OpenMP job on an exclusive node:

#!/bin/bash
#SBATCH --nodes=1
#SBATCH --exclusive

export OMP_NUM_THREADS=$SLURM_CPUS_ON_NODE
./omp_prog

Interactive job only

Please use -c, --cpus-per-task=X instead of -n, --ntasks=X to request an interactive job. Both result in an interactive job with X CPUs available but only the former option automatically assigns the correct number of threads to the OpenMP program. If  the option --ntasks is used only, the OpenMP program will use one thread or all threads will be bound to one CPU core. 

Hybrid (MPI + OpenMP)

An example of running a job for hybrid code:

#!/bin/bash
#SBATCH --nodes=2
#SBATCH --tasks-per-node=4
#SBATCH --cpus-per-task=12

# Run 4 MPI processes on each node and 12 OpenMP threads spawned from a MPI process
export OMP_NUM_THREADS=12
srun ./hybrid_prog

To run a job across either 40-core or 48-core nodes exclusively:

#!/bin/bash
#SBATCH --nodes=2
$SBATCH --tasks-per-node=4

# Run 4 MPI processes on each node and the maximum available OpenMP threads spawned from a MPI process 
export SLURM_CPUS_PER_TASK=$(($SLURM_CPUS_ON_NODE/$SLURM_NTASKS_PER_NODE))
export OMP_NUM_THREADS=$SLURM_CPUS_PER_TASK
srun ./hybrid_prog

Tuning Parallel Program Performance: Process/Thread Placement

To get the maximum performance, it is important to make sure that processes/threads are located as close as possible to their data, and as close as possible to each other if they need to work on the same piece of data, with given the arrangement of node, sockets, and cores, with different access to RAM and caches. 

While cache and memory contention between threads/processes are an issue, it is best to use scatter distribution for code. 

Processes and threads are placed differently depending on the computing resources you requste and the compiler and MPI implementation used to compile your code. For the former, see the above examples to learn how to run a job on exclusive nodes. For the latter, this section summarizes the default behavior and how to modify placement.

OpenMP only

For all three compilers (Intel, GNU, PGI), purely threaded codes do not bind to particular CPU cores by default. In other words, it is possible that multiple threads are bound to the same CPU core

The following table describes how to modify the default placements for pure threaded code:

DISTRIBUTION Compact Scatter/Cyclic
DESCRIPTION Place threads as closely as possible on sockets Distribute threads as evenly as possible across sockets
INTEL KMP_AFFINITY=compact KMP_AFFINITY=scatter
GNU OMP_PLACES=sockets[1] OMP_PROC_BIND=spread/close
PGI[2]

MP_BIND=yes
MP_BLIST="$(seq -s, 0 2 47),$(seq -s, 1 2 47)" 

MP_BIND=yes
  1. Threads in the same socket might be bound to the same CPU core.
  2. PGI LLVM-backend (version 19.1 and later) does not support thread/processors affinity on NUMA architecture. To enable this feature, compile threaded code with --Mnollvm to use proprietary backend.

MPI Only

For MPI-only codes, MVAPICH2 first binds as many processes as possible on one socket, then allocates the remaining processes on the second socket so that consecutive tasks are near each other.  Intel MPI and OpenMPI alternately bind processes on socket 1, socket 2, socket 1, socket 2 etc, as cyclic distribution.

For process distribution across nodes, all MPIs first bind as many processes as possible on one node, then allocates the remaining processes on the second node. 

The following table describe how to modify the default placements on a single node for MPI-only code with the command srun:

DISTRIBUTION
(single node)
Compact Scatter/Cyclic
DESCRIPTION Place processs as closely as possible on sockets Distribute process as evenly as possible across sockets
MVAPICH2[1] Default MV2_CPU_BINDING_POLICY=scatter
MVAPICH2
(2.3.4 &  later)
srun --cpu-bind="map_cpu:$(seq -s, 0 2 47),$(seq -s, 1 2 47)" Default
INTEL MPI srun --cpu-bind="map_cpu:$(seq -s, 0 2 47),$(seq -s, 1 2 47)" Default
OPENMPI srun --cpu-bind="map_cpu:$(seq -s, 0 2 47),$(seq -s, 1 2 47)" Default
  1. MV2_CPU_BINDING_POLICY will not work if MV2_ENABLE_AFFINITY=0 is set.

To distribute processes evenly across nodes, please set SLURM_DISTRIBUTION=cyclic.

Hybrid (MPI + OpenMP)

For Hybrid codes, each MPI process is allocated  OMP_NUM_THREADS cores and the threads of each process are bound to those cores. All MPI processes (as well as the threads bound to the process) behave as we describe in the previous sections. It means the threads spawned from a MPI process might be bound to the same core. To change the default process/thread placmements, please refer to the tables above. 

Summary

The above tables list the most commonly used settings for process/thread placement. Some compilers and Intel libraries may have additional options for process and thread placement beyond those mentioned on this page. For more information on a specific compiler/library, check the more detailed documentation for that library.

GPU Programming

164 Nvidia V100 GPUs are available on Pitzer.  Please visit our GPU documentation.

Reference

Supercomputer: 

Queues and Reservations

Here are the queues available on Pitzer.

Note that in SLURM, queues are known as partitions as well.
NAME MAX WALLTIME NODES AVAILABLE MIN JOB SIZE MAX JOB SIZE NOTES
Serial 168 hours Available minus reservations 1 core 1 node  
Longserial 336 hours Available minus reservations 1 core 1 node Restricted access
Parallel 96 hours Available minus reservations 2 nodes 40 nodes   
Longparallel TBD Available minus reservations 2 nodes TBD Not currently supported.
Hugemem 168 hours 4 nodes 1 core 1 node  
Largemem 168 hours 12 nodes 1 core 1 node  
Parallel hugemem TBD 4 nodes 2 nodes TBD Not currently supported.
Parallel largemem TBD 12 nodes 2 nodes TBD Not currently supported.
GPU serial 168 hours Available minus reservations 1 core 1 node Includes dual GPU and quad GPU nodes
GPU parallel 96 hours Available minus reservations 2 nodes 10 nodes Includes dual GPU and quad GPU nodes 
Debug-regular 1 hour 6 nodes 1 core 2 nodes --partition=debug
Debug-GPU 1 hour 2 nodes 1 core 2 nodes --partition=gpudebug

 

Note:

  • "Available minus reservations" means all standard dense or GPU compute nodes in the cluster currently operational (this will fluctuate slightly), less the reservations for specific projects.
  • To access one of the restricted queues, please contact OSC Help. Generally, access will only be granted to these queues if the performance of the job cannot be improved, and job size cannot be reduced by splitting or checkpointing the job.
  • Only up to 2 quad GPU nodes can be requested in a single job
Supercomputer: 
Service: 

Batch Limit Rules

Pitzer includes two types of processors, Intel® Xeon® 'Skylake' processor and Intel® Xeon® 'Cascade Lake' processor. This document provides you information on how to request resources based on the requirements of # of cores, memory, etc despite the heterogeneous nature of the Pitzer cluster. Therefore, in some cases, your job can land on either type of processor. Please check this page on how to request resources due to the heterogeneous nature and limit your job to a certain type of processor on Pitzer.
We use Slurm syntax for all the discussions on this page. Please check this page if your script is prepared in PBS syntax. 

Memory Limit:

It is strongly suggested to consider the memory use to the available per-core memory when users request OSC resources for their jobs. 

Regular Compute Node

  • For the regular 'Skylake' processor-based node, it has 40 cores/node. The physical memory equates to 4.8 GB/core or 192 GB/node; while the usable memory equates to 4556 MB/core or 178 GB/node.
  • For the regular 'Cascade Lake' processor-based node, it has 48 cores/node. The physical memory equates to 4.0 GB/core or 192 GB/node; while the usable memory equates to 3797 MB/core or 178 GB/node. 

Jobs requesting no more than 1 node

If your job requests less than a full node, it may be scheduled on a node with other running jobs. In this case, your job is entitled to a memory allocation proportional to the number of cores requested (4556 MB/core or 3797MB/core depending on which node your job lands on).  For example, without any memory request ( mem=XX ),

  • A job that requests --ntasks=1  and lands on 'Skylake' node will be assigned one core and should use no more than 4556 MB of RAM; a job that requests --ntasks=1  and lands on 'Cascade Lake' node will be assigned one core and should use no more than 3797 MB of RAM
  • A job that requests --ntasks=3  and lands on 'Skylake' node will be assigned 3 cores and should use no more than 3*4556 MB of RAM; a job that requests --ntasks=3  and lands on 'Cascade Lake' node will be assigned 3 cores and should use no more than 3*3797 MB of RAM
  • A job that requests  --ntasks=40  and lands on 'Skylake' node will be assigned the whole node (40 cores) with 178 GB of RAM; a job that requests --ntasks=40  and lands on 'Cascade Lake' node will be assigned 40 cores (partial node) and should use no more than 40* 3797 MB of RAM.  
Please be careful if you include memory request ( mem=XX ) in your job.

There is a known bug when using both --ntasks-per-node and --mem in the request so we suggest using only --mem or the combination of --ntasks and --mem (see this page for more information on the bug). 

  • A job that requests --ntasks=1 --mem=16000MB  and lands on 'Skylake' node will be assigned one core and have access to 16000 MB of RAM, and charged for 4 cores worth of usage; a job that requests --ntasks=1 --mem=16000MB  and lands on 'Cascade Lake' node will be assigned one core and have access to 16000 MB of RAM, and charged for 5 cores worth of usage
  • A job that requests --ntasks=8 --mem=16000MB  and lands on 'Skylake' node will be assigned 8 cores but have access to only 16000 MB of RAM , and charged for 8 cores worth of usage; a job that requests --ntasks=8 --mem=16000MB  and lands on 'Cascade Lake' node will be assigned 8 cores but have access to only 16000 MB of RAM , and charged for 8 cores worth of usage

Jobs requesting more than 1 node

A multi-node job ( --nodes > 1 ) will be assigned the entire nodes and charged for the entire nodes regardless of --ntasks or --ntasks-per-node request. For example, a job that requests --nodes=10 --ntasks-per-node=1  and lands on 'Skylake' node will be charged for 10 whole nodes (40 cores/node*10 nodes, which is 400 cores worth of usage); a job that requests --nodes=10 --ntasks-per-node=1  and lands on 'Cascade Lake' node will be charged for 10 whole nodes (48 cores/node*10 nodes, which is 480 cores worth of usage). We usually suggest not including --ntasks-per-node and using --ntasks if needed.   

Large Memory Node

On Pitzer, it has 48 cores per node. The physical memory equates to 16.0 GB/core or 768 GB/node; while the usable memory equates to 15,872 MB/core or 744 GB/node.

For any job that requests more than 363 GB/node but no more than 744 GB/node, the job will be scheduled on the large memory node. Please always specify a memory limit in your job if your job requests a large memory node using --mem, which is the total memory per node allocated to the job. You can request a partial large memory node, so consider your request more carefully when you plan to use a large memory node, and specify the memory based on what you will use. 

Huge Memory Node

On Pitzer, it has 80 cores per node. The physical memory equates to 37.5 GB/core or 3 TB/node; while the usable memory equates to 38,259 MB/core or  2989 GB/node.

For any job that requests more than 744 GB/node but no more than 2989 GB/node, the job will be scheduled on the large memory node. Please always specify a memory limit in your job if your job requests a huge memory node using --mem, which is the total memory per node allocated to the job. You can request a partial huge memory node, so consider your request more carefully when you plan to use a huge memory node, and specify the memory based on what you will use. 

Summary

In summary, for serial jobs, we will allocate the resources considering both the # of cores and the memory request. For parallel jobs (nodes>1), we will allocate the entire nodes with the whole memory regardless of other requests. Check the table in this page about the usable memory of different types of nodes on Pitzer. To manage and monitor your memory usage, please refer to Out-of-Memory (OOM) or Excessive Memory Usage

GPU Jobs

Dual GPU Node

  • For the dual GPU node with 'Skylake' processor, it has 40 cores/node. The physical memory equates to 9.6 GB/core or 384 GB/node; while the usable memory equates to 9292 MB/core or 363 GB/node. Each node has 2 NVIDIA Volta V100 w/ 16GB GPU memory. 
  • For the dual GPU node with 'Cascade Lake' processor, it has 48 cores/node. The physical memory equates to 8.0 GB/core or 384 GB/node; while the usable memory equates to 7744 MB/core or 363 GB/node. Each node has 2 NVIDIA Volta V100 w/32GB GPU memory.  

For serial jobs, we will allow node sharing on GPU nodes so a job may request either 1 or 2 GPUs (--ntasks=XX --gpus-per-node=1 or --ntasks=XX --gpus-per-node=2)

For parallel jobs (nodes>1), we will not allow node sharing. A job may request 1 or 2 GPUs ( gpus-per-node=1 or gpus-per-node=2 ) but both GPUs will be allocated to the job.

Quad GPU Node

For quad GPU node, it has 48 cores/node. The physical memory equates to 16.0 GB/core or 768 GB/node; while the usable memory equates to 15,872 MB/core or 744 GB/node.. Each node has 4 NVIDIA Volta V100s w/32GB GPU memory and NVLink.

For serial jobs, we will allow node sharing on GPU nodes, so a job can land on a quad GPU node if it requests 3-4 GPUs per node (--ntasks=XX --gpus-per-node=3 or --ntasks=XX --gpus-per-node=4), or requests quad GPU node explicitly with using --gpus-per-node=v100-quad:G, or gets backfilled with requesting 1-2 GPUs per node with less than 4 hours long. 

For parallel jobs (nodes>1), only up to 2 quad GPU nodes can be requested in a single job. We will not allow node sharing and all GPUs will be allocated to the job.

Walltime Limit

Here is the walltime limit for different queues/partitions available on Pitzer:

NAME

MAX WALLTIME

MIN JOB SIZE

MAX JOB SIZE

NOTES

Serial

168 hours

1 core

1 node

 

Longserial

336 hours

1 core

1 node

Restricted access

Parallel

96 hours

2 nodes

40 nodes 

 

Hugemem

168 hours

1 core

1 node

 

Largemem

168 hours

1 core

1 node

 

GPU serial

168 hours

1 core

1 node

Includes dual and quad GPU nodes

GPU parallel

96 hours

2 nodes

10 nodes

Includes and quad GPU nodes 

Debug-regular

1 hour

1 core

2 nodes

-q debug

Debug-GPU

1 hour

1 core

2 nodes

-q debug

Job/Core Limits

  Max Running Job Limit Max Core Limit
Individual User 256 2160
Project/Group 384 2160

An individual user can have up to the max concurrently running jobs and/or up to the max processors/cores in use. 

However, among all the users in a particular group/project, they can have up to the max concurrently running jobs and/or up to the max processors/cores in use.

A user may have no more than 1000 jobs submitted to both the parallel and serial job queue separately.
Supercomputer: 
Service: 

Citation

For more information about citations of OSC, visit https://www.osc.edu/citation.

To cite Pitzer, please use the following Archival Resource Key:

ark:/19495/hpc56htp

Please adjust this citation to fit the citation style guidelines required.

Ohio Supercomputer Center. 2018. Pitzer Supercomputer. Columbus, OH: Ohio Supercomputer Center. http://osc.edu/ark:19495/hpc56htp

Here is the citation in BibTeX format:

@misc{Pitzer2018,
ark = {ark:/19495/hpc56htp},
url = {http://osc.edu/ark:/19495/hpc56htp},
year  = {2018},
author = {Ohio Supercomputer Center},
title = {Pitzer Supercomputer}
}

And in EndNote format:

%0 Generic
%T Pitzer Supercomputer
%A Ohio Supercomputer Center
%R ark:/19495/hpc56htp
%U http://osc.edu/ark:/19495/hpc56htp
%D 2018

Here is an .ris file to better suit your needs. Please change the import option to .ris.

Documentation Attachment: 
Supercomputer: 

Pitzer SSH key fingerprints

These are the public key fingerprints for Pitzer:
pitzer: ssh_host_rsa_key.pub = 8c:8a:1f:67:a0:e8:77:d5:4e:3b:79:5e:e8:43:49:0e 
pitzer: ssh_host_ed25519_key.pub = 6d:19:73:8e:b4:61:09:a9:e6:0f:e5:0d:e5:cb:59:0b 
pitzer: ssh_host_ecdsa_key.pub = 6f:c7:d0:f9:08:78:97:b8:23:2e:0d:e2:63:e7:ac:93 


These are the SHA256 hashes:​
pitzer: ssh_host_rsa_key.pub = SHA256:oWBf+YmIzwIp+DsyuvB4loGrpi2ecow9fnZKNZgEVHc 
pitzer: ssh_host_ed25519_key.pub = SHA256:zUgn1K3+FK+25JtG6oFI9hVZjVxty1xEqw/K7DEwZdc 
pitzer: ssh_host_ecdsa_key.pub = SHA256:8XAn/GbQ0nbGONUmlNQJenMuY5r3x7ynjnzLt+k+W1M 

Supercomputer: 

Migrating jobs from other clusters

This page includes a summary of differences to keep in mind when migrating jobs from other clusters to Pitzer. 

Guidance for Oakley Users

The Oakley cluster is removed from service on December 18, 2018. 

Guidance for Owens Users

Hardware Specifications

  pitzer (PER NODE) owens (PER NODE)
Regular compute node

40 cores and 192GB of RAM

48 cores and 192GB of RAM

28 cores and 125GB of RAM
Huge memory node

48 cores and 768GB of RAM

(12 nodes in this class)

80 cores and 3.0 TB of RAM

(4 nodes in this class)

48 cores and 1.5TB of RAM

(16 nodes in this class)

File Systems

Pitzer accesses the same OSC mass storage environment as our other clusters. Therefore, users have the same home directory, project space, and scratch space as on the Owens cluster.

Software Environment

Pitzer uses the same module system as Owens.

Use   module load <package to add a software package to your environment. Use   module list   to see what modules are currently loaded and  module avail   to see the modules that are available to load. To search for modules that may not be visible due to dependencies or conflicts, use   module spider 

You can keep up to on the software packages that have been made available on Pitzer by viewing the Software by System page and selecting the Pitzer system.

Programming Environment

Like Owens, Pitzer supports three compilers: Intel, PGI, and gnu. The default is Intel. To switch to a different compiler, use  module swap intel gnu  or  module swap intel pgi

Pitzer also use the MVAPICH2 implementation of the Message Passing Interface (MPI), optimized for the high-speed Infiniband interconnect and support the Advanced Vector Extensions (AVX2) instruction set.

See the Pitzer Programming Environment page for details. 

Accounting

Below is a comparison of job limits between Pitzer and Owens:

  PItzer Owens
Per User Up to 256 concurrently running jobs and/or up to 2160 processors/cores in use  Up to 256 concurrently running jobs and/or up to 3080 processors/cores in use
Per group Up to 384 concurrently running jobs and/or up to 2160 processors/cores in use Up to 384 concurrently running jobs and/or up to 4620 processors/cores in use

Please see Queues and Reservations for Pitzer and Batch Limit Rules for more details.

Guidance for Ruby Users

The Ruby cluster is removed from service on October 29, 2020. 
Supercomputer: 
Service: 

Guidance on Requesting Resources on Pitzer

In late 2018, OSC installed 260 Intel® Xeon® 'Skylake' processor-based nodes as the original Pitzer cluster. In September 2020, OSC installed additional 398 Intel® Xeon® 'Cascade Lake' processor-based nodes as part of a Pitzer Expansion cluster. This expansion makes Pitzer a heterogeneous cluster, which means that the jobs may land on different types of CPU and behaves differently if the user submits the same job script repeatedly to Pitzer but does not request the resources properly. This document provides you some general guidance on how to request resources on Pitzer due to this heterogeneous nature. 

Step 1: Identify your job type

  Nodes the job may be allocated on # of cores per node Usable Memory GPU
Jobs requesting standard compute node(s) Dual Intel Xeon 6148s Skylake @2.4GHz 40 

178 GB memory/node

4556 MB memory/core

N/A
Dual Intel Xeon 8268s Cascade Lakes @2.9GHz 48

178 GB memory/node

3797 MB memory/core

N/A
Jobs requesting dual GPU node(s)

Dual Intel Xeon 6148s Skylake @2.4GHz

40

363 GB memory/node

9292 MB memory/core

2 NVIDIA Volta V100 w/ 16GB GPU memory
Dual Intel Xeon 8268s Cascade Lakes @2.9GHz 48

363 GB memory/node

7744 MB memory/core

2 NVIDIA Volta V100 w/32GB GPU memory
Jobs requesting quad GPU node(s) Dual Intel Xeon 8260s Cascade Lakes @2.4GHz 48

744 GB memory/node

15872 MB memory/core

4 NVIDIA Volta V100s w/32GB GPU memory and NVLink
Jobs requesting large memory node(s) Dual Intel Xeon 8268s Cascade Lakes @2.9GHz 48

744 GB memory/node

15872 MB memory/core

N/A
Jobs requesting huge memory node(s) Quad Processor Intel Xeon 6148 Skylakes @2.4GHz 80

2989 GB memory/node

38259 MB memory/core

N/A

According to this table,

  • If your job requests standard compute node(s) or dual GPU node(s), it can potentially land on different types of nodes and may result in different job performance. Please follow the steps below to determine whether you would like to restrain your job to a certain type of node(s). 
  • If your job requests quad GPU node(s), large memory node(s), or huge memory node(s), please check this page on how to request these special types of resources properly. 

Step 2: Perform test

This step is to submit your jobs requesting the same resources to different types of nodes on Pitzer. For your job script is prepared with either PBS syntax or Slurm syntax:

  • Add the line #SBATCH --constraint=40core and save the script as job_40core.txt. This job will land on node(s) with dual Intel Xeon 6148s Skylake, (and NVIDIA Volta V100 w/ 16GB GPU memory if it is a GPU job)
  • Add the line #SBATCH --constraint=48core and save the script as job_48core.txt. This job will land on node(s) with dual Intel Xeon 8268s Cascade Lake, (and NVIDIA Volta V100 w/32GB GPU memory if it is a GPU job)

Once the script is ready, submit your jobs to Pitzer and wait till the jobs are completed. 

Step 3: Compare the results

Once the jobs are completed, you can compare the job performances in terms of core-hours, gpu-hours, walltime, etc. to determine how your job is sensitive to the type of the nodes. If you would like to restrain your job to land on a certain type of nodes based on the testing, you can add  #SBATCH --constraint=. The disadvantage of this is that you may have a longer queue wait time on the system. If you would like to have your jobs scheduled as fast as possible and do not care which type of nodes your job will land on, do not include the constraint in the job request. 

Supercomputer: 

GPU Computing

OSC offers GPU computing on all its systems.  While GPUs can provide a significant boost in performance for some applications the computing model is very different from the CPU.  This page will discuss some of the ways you can use GPU computing at OSC.

Accessing GPU Resources

To request nodes with a GPU add the --gpus-per-node=x attribute to the directive in your batch script, for example, on Owens:

#SBATCH --gpus-per-node=1

In most cases you'll need to load the cuda module (module load cuda) to make the necessary Nvidia libraries available.

Setting the GPU compute mode (optional)

The GPUs on Owens and Pitzer can be set to different compute modes as listed here.  They can be set by adding the following to the GPU specification when using the srun command. By default it is set to exclusive.

srun --gpu_cmode=shared
#or
srun --gpu_cmode=exclusive

The compute mode exclusive is the default on GPU nodes if a compute mode is not specified. With this compute mode, mulitple CUDA processes on the same GPU device are not allowed.

Using GPU-enabled Applications

We have several supported applications that can use GPUs.  This includes

Please see the software pages for each application.  They have different levels of support for multi-node jobs, cpu/gpu work sharing, and environment set-up.

Libraries with GPU Support

There are a few libraries that provide GPU implementations of commonly used routines. While they mostly hide the details of using a GPU there are still some GPU specifics you'll need to be aware of, e.g. device initialization, threading, and memory allocation.

MAGMA

MAGMA is an implementation of BLAS and LAPACK with multi-core (SMP) and GPU support. There are some differences in the API of standard BLAS and LAPACK.

cuBLAS and cuSPARSE

cuBLAS is a highly optimized BLAS from NVIDIA. There are a few versions of this library, from very GPU-specific to nearly transparent. cuSPARSE is a BLAS-like library for sparse matrices.

The MAGMA library is built on cuBLAS.

cuFFT

cuFFT is NVIDIA's Fourier transform library with an API similar to FFTW.

cuDNN

cuDNN is NVIDIA's Deep Neural Network machine learning library. Many ML applications are built on cuDNN.

Direct GPU Programming

GPUs present a different programming model from CPUs so there is a significant time investment in going this route.

OpenACC

OpenACC is a directives-based model similar to OpenMP. Currently this is only supported by the Portland Group C/C++ and Fortran compilers.

OpenCL

OpenCL is a set of libraries and C/C++ compiler extensions supporting GPUs (NVIDIA and AMD) and other hardware accelerators. The CUDA module provides an OpenCL library.

CUDA

CUDA is the standard NVIDIA development environment. In this model explicit GPU code is written in the CUDA C/C++ dialect, compiled with the CUDA compiler NVCC, and linked with a native driver program.

About OSC GPU Hardware

Our GPUs span several generations with different capabilites and ease-of-use. Many of the differences won't be visible when using applications or libraries, but some features and applications may not be supported on the older models.

Owens P100

The P100 "Pascal" is a NVIDIA GPU with a compute capability of 6.0. The 6.0 capability includes unified shared CPU/GPU memory -- the GPU now has its own virtual memory capability and can map CPU memory into its address space.

Each P100 has 16GB of on-board memory and there is one GPU per GPU node.

Pitzer V100 (16 and 32GB)

The V100 "Volta" is NVIDIA's flagship GPU with a compute capability of 7.0.

V100 deployed in 2018 has 16GB of memory.

V100 deployed in 2020 has 32GB of memory.

There are two GPUs per GPU node.

Pitzer quad V100

Quad NVIDIA Volta V100s w/32GB GPU memory and NVLink.

There are four GPUs per GPU node.

Examples

There are example jobs and code at GitHub

 

Tutorials & Training

Training is an important part of our services. We are working to expand our portfolio; we currently provide the following:

  • Training classes. OSC provides training classes, at our facility, on-site and remotely.
  • HOWTOs. Step-by-step guides to accomplish certain tasks on our systems.
  • Tutorials. Online content designed for self-paced learning.

Other good sources for information:

  • Knowledge Base.  Useful information that does not fit our existing documentation.
  • FAQ.  List of commonly asked questions.

Batch Processing at OSC

OSC has recently switched schedulers from PBS to Slurm.
Please see the slurm migration pages for information about how to convert commands.

Batch processing

Efficiently using computing resources at OSC requires using the batch processing system. Batch processing refers to submitting requests to the system to use computing resources.

The only access to significant resources on the HPC machines is through the batch process. This guide will provide an overview of OSC's computing environment, and provide some instruction for how to use the batch system to accomplish your computing goals.

The menu at the right provides links to all the pages in the guide, or you can use the navigation links at the bottom of the page to step through the guide one page at a time. If you need additional assistance, please do not hesitate to contact OSC Help.

Batch System Concepts

The only access to significant resources on the HPC machines is through the batch process.

Why use a batch system?

Access to the OSC clusters is through a system of login nodes. These nodes are reserved solely for the purpose of managing your files and submitting jobs to the batch system. Acceptable activities include editing/creating files, uploading and downloading files of moderate size, and managing your batch jobs. You may also compile and link small-to-moderate size programs on the login nodes.

CPU time and memory usage are severely limited on the login nodes. There are typically many users on the login nodes at one time. Extensive calculations would degrade the responsiveness of those nodes.

If a process is started on the login nodes that is using too much cpu or memory, then it may be killed without warning.

The batch system allows users to submit jobs requesting the resources (nodes, processors, memory, GPUs) that they need. The jobs are queued and then run as resources become available. The scheduling policies in place on the system are an attempt to balance the desire for short queue waits against the need for efficient system utilization.

Interactive vs. batch

When you type commands in a login shell and see a response displayed, you are working interactively. To run a batch job, you put the commands into a text file instead of typing them at the prompt. You submit this file to the batch system, which will run it as soon as resources become available. The output you would normally see on your display goes into a log file. You can check the status of your job interactively and/or receive emails when it begins and ends execution.

Terminology

The batch system used at OSC is SLURM. A central manager slurmctld, monitors resources and work. You’ll need to understand the terms cluster, node,  and processor (core) in order to request resources for your job. See HPC basics if you need this background information.

The words “parallel” and “serial” as used by SLURM can be a little misleading. From the point of view of the batch system a serial job is one that uses just one node, regardless of how many processors it uses on that node. Similarly, a parallel job is one that uses more than one node. More standard terminology considers a job to be parallel if it involves multiple processes.

Batch processing overview

Here is a very brief overview of how to use the batch system.

Choose a cluster

Before you start preparing a job script you should decide which cluster you want your job to run on, Owens or Pitzer. This decision will probably be based on the resources available on each system. Remember which cluster you’re using because the batch systems are independent.

Prepare a job script

Your job script is a text file that includes SLURM directives as well as the commands you want executed. The directives tell the batch system what resources you need, among other things. The commands can be anything you would type at the login prompt. You can prepare the script using any editor.

Submit the job

You submit your job to the batch system using the sbatch command, with the name of the script file as the argument. The sbatch command responds with the job ID that was given to your job, typically a 6- or 7-digit number.

Wait for the job to run

Your job may wait in the queue for minutes or days before it runs, depending on system load and the resources requested. It may then run for minutes or days. You can monitor your job’s progress or just wait for an email telling you it has finished.

Retrieve your output

The log file (screen output) from your job will be in the directory you submitted the job from by default. Any other output files will be wherever your script put them.

Supercomputer: 

Batch Execution Environment

Shell and initialization

Your batch script executes in a shell on a compute node. The environment is identical to what get when you connect to a login node except that you have access to all the resources requested by your job. The shell that slurm uses is determined by the first line of the job script #!/bin/bash. The appropriate “dot-files” ( .login , .profile , .cshrc ) will be executed, the same as when you log in. (For information on overriding the default shell, see the Job Scripts section.)

The job begins in the directory that it was submitted from. You can use the cd command to change to a different directory. The environment variable $SLURM_SUBMIT_DIR makes it easy to return to the directory from which you submitted the job:

cd $SLURM_SUBMIT_DIR

Modules

There are dozens of software packages available on OSC’s systems, many of them with multiple versions. You control what software is available in your environment by loading the module for the software you need. Each module sets certain environment variables required by the software.

If you are running software that was installed by OSC, you should check the software documentation page to find out what modules to load.

Several modules are automatically loaded for you when you login or start a batch script. These default modules include

  • modules required by the batch system
  • the Intel compiler suite
  • an MPI package compatible with the default compiler (for parallel computing)

The module command has a number of subcommands. The most useful of these are documented here. For more details, type module help.

Certain modules are incompatible with each other and should never be loaded at the same time. Examples are different versions of the same software or multiple installations of a library built with different compilers.

Note to those who build or install their own software: Be sure to load the same modules when you run your software that you had loaded when you built it, including the compiler module.

Each module has both a name and a software version number. When more than one version is available for the same name, one of them is designated as the default. For example, the following modules are available for the Intel compilers on Owens:  (Note:  The versions shown are out of date but the concept is the same.)

  • intel/12.1.0 (default)
  • intel/12.1.4.319

If you specify just the name, it refers to the default version or the currently loaded version, depending on the context. If you want a different version, you must give the entire string. Examples are given below.

You can have only one compiler module loaded at a time, either intel, pgi, or gnu. The intel module is loaded initially; to change to pgi or gnu, do a module swap (see example below).

Some software libraries have multiple installations built for use with different compilers. The module system will load the one compatible with the compiler you have loaded. If you swap compilers, all the compiler-dependent modules will also be swapped.

Special note to gnu compiler users: While the gnu compilers are always in your path, you should load the gnu compiler module to ensure you are linking to the correct library versions.

To list the modules you have loaded:

module list

To see all modules that are compatible with your currently loaded modules:

module avail

To see compatible modules whose names start with fftw:

module avail fftw

To see all possible modules:

module spider

To see all possible modules whose names start with fftw:

module spider fftw

To load the fftw3 module that is compatible with your current compiler:

module load fftw3

To unload the fftw3 module:

module unload fftw3

To load the default version of the abaqus module (not compiler-dependent):

module load abaqus

To load a different version of the abaqus module:

module load abaqus/6.8-4

To unload whatever abaqus module you have loaded:

module unload abaqus

To swap the intel compilers for the pgi compilers (unloads intel, loads pgi):

module swap intel pgi

To swap the default version of the intel compilers for a different version:

module swap intel intel/12.1.4.319

To display help information for the mkl module:

module help mkl

To display the commands run by the mkl module:

module show mkl

To use a locally installed module, first import the module directory:

module use [/path/to/modulefiles]

And then load the module:

module load localmodule

SLURM environment variables

Your batch execution environment has all the environment variables that your login environment has plus several that are set by the batch system. This section gives examples for using some of them. For more information see man sbatch.

Directories

Several directories may be useful in your job.

The absolute path of the directory your job was submitted from is $SLURM_SUBMIT_DIR. Recall that your job always starts in your home directory. To get back to your submission directory:

cd $SLURM_SUBMIT_DIR

Each job has a temporary directory, $TMPDIR , on the local disk of each node assigned to it. Access to this directory is much faster than access to your home or project directory. The files in this directory are not visible from all the nodes in a parallel job; each node has its own directory. The batch system creates this directory when your job starts and deletes it when your job ends. To copy file input.dat to $TMPDIR on all your job’s first node:

cp input.dat $TMPDIR

To copy file input.dat to $TMPDIR on all your job’s nodes:

sbcast input.dat $TMPDIR/input.dat

Each job has a temporary directory, $PFSDIR , on the parallel file system, if users add node attribute "pfsdir" in the batch request (nodes=XX:ppn=XX:pfsdir). This is a single directory shared by all the nodes a job is running on. Access is faster than access to your home or project directory but not as fast as $TMPDIR . The batch system creates this directory when your job starts and deletes it when your job ends. To copy the file output.dat from this directory to the directory you submitted your job from:

cp $PFSDIR/output.dat $SLURM_SUBMIT_DIR

The $HOME environment variable refers to your home directory. It is not set by the batch system but is useful in some job scripts. It is better to use $HOME than to hardcode the path to your home directory. To access a file in your home directory:

cat $HOME/myfile

Job information

Specific information about your job that may be useful can be obtained from

A list of the nodes and cores assigned to your job is obtained using srun hostname |sort -n

For GPU jobs, a list of the GPUs assigned to your job is in the file $SLURM_GPUS_ON_NODE. To display this file:

cat $SLURM_GPUS_ON_NODE

If you use a job array, each job in the array gets its identifier within the array in the variable $SLURM_ARRAY_JOB_ID. To pass a file name parameterized by the array ID into your application:

./a.out input${$SLURM_ARRAY_JOB_ID}.dat

To display the numeric job Identifier assigned by the batch system:

echo $SLURM_JOB_ID

To display the job name:

echo $SLURM_JOB_NAME

Use fast storage

If your job does a lot of file-based input and output, your choice of file system can make a huge difference in the performance of the job.

Shared file systems

Your home and project directories are located on shared file systems, providing long-term storage that is accessible from all OSC systems. Shared file systems are relatively slow. They cannot handle heavy loads such as those generated by large parallel jobs or many simultaneous serial jobs. You should minimize the I/O your jobs do on the shared file systems. It is usually best to copy your input data to fast temporary storage, run your program there, and copy your results back to your home or project directory.

Batch-managed directories

Batch-managed directories are temporary directories that exist only for the duration of a job. They exist on two types of storage: disks local to the compute nodes and a parallel file system.

A big advantage of batch-managed directories is that the batch system deletes them when a job ends, preventing clutter on the disk.

A disadvantage of batch-managed directories is that you can’t access them after your job ends. Be sure to include commands in your script to copy any files you need to long-term storage. To avoid losing your files if your job ends abnormally, for example by hitting its walltime limit, include a trap command in your script (Note:  trap  commands do not work in csh and tcsh shell batch scripts). The following example creates a subdirectory in $SLURM_SUBMIT_DIR and copies everything from $TMPDIR into it in case of abnormal termination.

trap "cd $SLURM_SUBMIT_DIR;mkdir $SLURM_JOB_ID;cp -R $TMPDIR/* $SLURM_SUBMIT_DIR;exit" TERM

If a node your job is running on crashes, the trap command may not be executed. It may be possible to recover your batch-managed directories in this case. Contact OSC Help for assistance.  For other details on retrieving files from unexpectedly terminated jobs see this FAQ.

Local disk space

The fastest storage is on a disk local to the node your job is running on, accessed through the environment variable $TMPDIR . The main drawback to local storage is that each node of a parallel job has its own directory and cannot access the files on other nodes. See also “Considerations for Parallel Jobs”.

Local disk space should be used only through the batch-managed directory created for your job. Please do not use /tmp directly because your files won’t be cleaned up properly.

Parallel file system

The parallel file system is faster than the shared file systems for large-scale I/O and can handle a much higher load. You should use it when your files must be accessible by all the nodes in your job and also when your files are too large for the local disk.

The parallel file system is efficient for reading and writing data in large blocks. It should not be used for I/O involving many small accesses.

The parallel file system is typically used through the batch-managed directory created for your job. The path for this directory is in the environment variable $PFSDIR .

You may also create a directory for yourself in /fs/scratch  and use it the way you would use any other directory. You should name the directory with either your user name or your project ID. This directory will not be backed up; files are subject to deletion after some number of months (see policies for details).

Note: You should not copy your executable files to $PFSDIR. They should be run from your home or project directories or from $TMPDIR.

Supercomputer: 

Job Scripts

A job script is a text file containing job setup information for the batch system followed by commands to be executed. It can be created using any text editor and may be given any name. Some people like to name their scripts something like myscript.job or myscript.sh, but myscript works just as well.

A job script is simply a shell script. It consists of SLURM directives, comments, and executable statements. The # character indicates a comment, although lines beginning with #SBATCH are interpreted as SLURM directives. Blank lines can be included for readability.

SBATCH header lines

At the top of a job script are several lines starting with #SBATCH . These are SLURM SBATCH directives or header lines. They provide job setup information used by SLURM, including resource requests, email options, and more. The header lines may appear in any order, but they must precede any executable lines in your script. Alternatively you may provide these directives (without the #SBATCH notation) on the command line with the sbatch command.

$ sbatch --jobname=test_job myscript.sh

Resource limits

Options used to request resources, including nodes, memory, time, and software flags, as described below.

Walltime

The walltime limit is the maximum time your job will be allowed to run, given in seconds or hours:minutes:seconds. This is elapsed time. If your job exceeds the requested time, the batch system will kill it. If your job ends early, you will be charged only for the time used.

The default value for walltime is 1:00:00 (one hour).

To request 20 hours of wall clock time:

#SBATCH --time=20:00:00

It is to your advantage to come up with a good estimate of the time your job will take. An underestimate will lead to your job being killed. A large overestimate may prevent your job from being backfilled, or fit into an empty time slot.

Tasks (cores), nodes and gpus

The tasks and nodes resource limit specifies not just the number of nodes but also the properties of those nodes. The properties are different on different clusters but may include the number of cores per node, the number of GPUs per node (gpus), and the type of node.

The default is --nodes=1 and --ntasks=1, but this fails under some circumstances.

To request a single processor (sequential job):

#SBATCH --ntasks=1

To request one whole 40 core node on Pitzer:

#SBATCH --ntasks=40
#SBATCH --constraint=40core

To request 4 whole 40 core nodes on Pitzer:

#SBATCH --nodes=4
#SBATCH --ntasks-per-node=40
#SBATCH --constraint=40core

To request 10 nodes with 2 GPUs each on Pitzer:

#SBATCH --nodes=4
#SBATCH --ntasks-per-node=40
#SBATCH --gpus-per-node=2
#SBATCH --constraint=40core

To request 1 node with use of 6 cores and 1 GPU on Pitzer:

#SBATCH --ntasks=6
#SBATCH --gpus-per-node=1

Note: Under our current scheduling policy parallel jobs are always given full nodes. You can easily use just part of each node even if you request the whole thing (see the -ppn option on mpiexec).

Memory

The memory limit is the total amount of memory needed across all nodes. There is no need to specify a memory limit unless your memory requirements are disproportionate to the number of cores you are requesting or you need a large-memory node. For parallel jobs you must multiply the memory needed per node by the number of nodes to get the correct limit; you should usually request whole nodes and omit the memory limit.

Default units are bytes, but values are usually expressed in megabytes (mem=4000MB) or gigabytes (mem=4GB).

To request 4GB memory (see note below):

#SBATCH mem=4gb

or

#SBATCH mem=4000mb

To request 24GB memory:

#SBATCH mem=24000mb

Note: The amount of memory available per node is slightly less than the nominal amount. If you want to request a fraction of the memory on a node, we recommend you give the amount in MB, not GB; 24000MB is less than 24GB. (Powers of 2 vs. powers of 10 -- ask a computer science major.)

Software licenses

If you are using a software package with a limited number of licenses, you should include the license requirement in your script. See the OSC documentation for the specific software package for details.

Example requesting five abaqus licenses:

#SBATCH --licenses=abaqus@osc:5

Job name

You can optionally give your job a meaningful name. The default is the name of the batch script, or just "sbatch" if the script is read on sbatch's standard input. The job name is used as part of the name of the job log files; it also appears in lists of queued and running jobs. The name may be up to 15 characters in length, no spaces are allowed, and the first character must be alphabetic.

Example:

#SBATCH --job-name=my_first_job

Mail options

You may choose to receive email when your job begins, when it ends, and/or when it fails. The email will be sent to the address we have on record for you. You should use only one --mail-type=<type> directive and include all the options you want.

To get email when your job begins, ends or fails:

#SBATCH --mail-type=BEGIN,END,FAIL

To get email for all types use:

#SBATCH --mail-type=ALL

The default user emailed is the submitting user, but others can also be included:

#SBATCH --mail-user=osu1234,osu4321

Job log files

By default, SLURM returns one log file for the standard output stream (stdout) and for the standard error stream (stderr). You can also optionally specify names for the log files.

For job 123456, the output log will be named slurm-123456.out

Identify Project

It is required for a job script to specify a project account.

Current projects that are able to be used can be seen using the OSCfinger command and looking at the SLURM accounts section:

OSCfinger userex
Login: userex                                     Name: User Example
Directory: /users/PAS1234/userex (CREATED)       Shell: /bin/bash
E-mail: user-ex@osc.edu
Contact Type: REGULAR
Primary Group: pas1234
Groups: pas1234,pas4321
Institution: Ohio Supercomputer Center
Password Changed: Dec 11 2020 21:05               Password Expires: Jan 12 2021 01:05 AM
Login Disabled: FALSE                             Password Expired: FALSE
SLURM Enabled: TRUE
SLURM Clusters: owens,pitzer
* SLURM Accounts: pas1234,pas4321 *
SLURM Default Account: pas1234
Current Logins:
---

To specify an account use:

#SBATCH --account=PAS4321

For more details on errors you may see when you submit a job, see messages from sbatch.

Executable section

The executable section of your script comes after the header lines. The content of this section depends entirely on what you want your job to do. We mention just two commands that you might find useful in some circumstances. They should be placed at the top of the executable section if you use them.

The set -x command (set echo in csh) is useful for debugging your script. It causes each command in the batch file to be printed to the log file as it is executed, with a + in front of it. Without this command, only the actual display output appears in the log file.

To echo commands in bash or ksh:

set -x

To echo commands in tcsh or csh:

set echo on

The trap command allows you to specify a command to run in case your job terminates abnormally, for example if it runs out of wall time.

trap commands do not work in csh and tcsh shell batch scripts.

It is typically used to copy output files from a temporary directory to a home or project directory. The following example creates a directory in $SLURM_SUBMIT_DIR and copies everything from $TMPDIR into it. This executes only if the job terminates abnormally.

trap "cd $SLURM_SUBMIT_DIR;mkdir $SLURM_JOB_ID;cp -R $TMPDIR/* $SLURM_JOB_ID;exit" TERM

For other details on retrieving files from unexpectedly terminated jobs see this FAQ.

Considerations for parallel jobs

Each processor on our system is fast, but the real power of supercomputing comes from putting multiple processors to work on a task. This section addresses issues related to multithreading and parallel processing as they affect your batch script. For a more general discussion of parallel computing see another document.

Multithreading involves a single process, or program, that uses multiple threads to take advantage of multiple cores on a single node. The most common approach to multithreading on HPC systems is OpenMP. The threads of a process share a single memory space.

The more general form of parallel processing involves multiple processes, usually copies of the same program, which may run on a single node or on multiple nodes. These processes have separate memory spaces. If they communicate or share data, it is most commonly done through the Message-Passing Interface (MPI).

A program may use multiple levels of parallelism, employing MPI to communicate between nodes and OpenMP to utilize multiple processors on each node.

While many executables will run on any of our clusters, MPI programs must be built on the system they will run on. Most scientific programs will run faster if they are built on the system where they’re going to run.

Script issues in parallel jobs

In a parallel job your script executes on just the first node assigned to the job, so it’s important to understand how to make your job execute properly in a parallel environment. These notes apply to jobs running on multiple nodes.

You can think of the commands (executable lines) in your script as falling into four categories.

  • Commands that affect only the shell environment. These include such things as cd , module , and export (or setenv ). You don’t have to worry about these. The commands are executed on just the first node, but the batch system takes care of transferring the environment to the other nodes.
  • Commands that you want to have execute on only one node. These might include date or echo . (Do you really want to see the date printed 20 times in a 20-node job?) They might also include cp if your parallel program expects files to be available only on the first node. You don’t have to do anything special for these commands.
  • Commands that have parallel execution, including knowledge of the batch system, built in. These include sbcast (parallel file copy) and some application software installed by OSC. You should consult the software documentation for correct parallel usage of application software.
  • Any other command or program that you want to have execute in parallel must be run using mpiexec. Otherwise it will run on only one node, while the other nodes assigned to the job will remain idle. See examples below.

mpiexec

The mpiexec command is used to run multiple copies of an executable program, usually (but not always) on multiple nodes. It is a replacement for the mpirun script which is part of the mpich package. Message-passing (MPI) programs must always be started with mpiexec .

Very important note: The mpiexec command installed at OSC is customized to work with the OSC environment and with our batch system. Other versions will not work correctly on our systems.

Note: The options below apply to the MVAPICH2 and IntelMPI installations at OSC. See the OpenMPI software page for mpiexec usage with OpenMPI.

The mpiexec command has the form:

mpiexec [mpiexec-options] progname [prog-args]

where mpiexec-options is a list of options to mpiexec, progname is the program you want to run, and prog-args is a list of arguments to the program. Note that if the program is not in your path, you must specify the path as part of the name. If the program is in your current working directory, you can put ./ in front of progname instead of adding it to your path. 

By default, mpiexec runs as many copies of progname as there are processors (cores) assigned to the job (nodes x ppn). For example, if your job requested --nodes=4 --ntasks-per-node=40, the following command will run 160 a.out processes:

mpiexec a.out

The example above can be modified to pass arguments to a.out. The following example shows two arguments:

mpiexec a.out abc.dat 123

If your program is multithreaded, or if it uses a lot of memory, it may be desirable to run just one process per node. The -ppn 1 option does this. Modifying the above example again, the following example would run 4 copies of a.out, one on each node:

mpiexec -ppn 1 a.out abc.dat 123

You can specify how many processes to run per node using the -ppn option. You cannot specify more processes per node than the number of cores your job requested per node (ppn value).To run 2 processes per node:

mpiexec -ppn 2 a.out abc.dat 123

It is also possible to specify the total number of processes to run using the -n or -np option. (These are the same thing.) This option is useful primarily for single-node jobs because it does not necessarily spread the processes out evenly over all the nodes. For example, if your job requested ntasks=40, the following command will run 4 a.out processes:

mpiexec -n 4 a.out abc.dat 123

The -tv option on mpiexec runs your program with the TotalView parallel debugger. For example, assuming --nodes=4 --ntasks-per-node=40, the following command lets you debug your program a.out with one process per node and the arguments given:

mpiexec -tv -ppn 1 a.out abc.dat 123

System commands can also be run with mpiexec. The following commands create a directory named data in the $TMPDIR directory on each node:

cd $TMPDIR
mpiexec -ppn 1 mkdir data

pbsdcp

If you use $TMPDIR in a parallel job, you will probably want to copy files to or from all the nodes in your job. The pbsdcp (“PBS Distributed Copy”) command is used for this task.

The following examples illustrate how to copy two files, a directory (recursively), and all files starting with “model” from your current directory to all the nodes assigned to your job.

pbsdcp file1 file2 $TMPDIR
pbsdcp -r dir1 $TMPDIR
pbsdcp model* $TMPDIR

The following example illustrates how to copy all files starting with “outfile” from all the nodes assigned to your job back to the directory you submitted your job from. The files from all the nodes will be placed into a single directory; you should name them differently to avoid name collisions. The quotes are necessary in gather mode ( -g ) if you use a wildcard (*) in your file name.

pbsdcp -g '$TMPDIR/outfile*' $PBS_O_WORKDIR

Environment variables for MPI

If your program combines MPI and OpenMP (or another multithreading technique), you should disable processor affinity by setting the environment variable $MV2_ENABLE_AFFINITY to 0 in your script. If you don’t disable affinity, all your threads will run on the same core, negating any benefit from multithreading.

To set the environment variable in bash, include this line in your script:

export MV2_ENABLE_AFFINITY=0

To set the environment variable in csh, include this line in your script:

setenv MV2_ENABLE_AFFINITY 0

Environment variables for OpenMP

The number of threads used by an OpenMP program is typically controlled by the environment variable $OMP_NUM_THREADS. If this variable isn't set, the number of threads defaults to the number of cores you requested per node (ppn value), although it can be overridden by the program.

If your job runs just one process per node and is the only job running on the node, the default behavior is what you want. Otherwise you should set $OMP_NUM_THREADS to a value that ensures that the total number of threads for all your processes on the node does not exceed the ppn value your job requested.

For example, to set the environment variable to a value of 40 in bash, include this line in your script:

export OMP_NUM_THREADS=40

For example, to set the environment variable to a value of 40 in csh, include this line in your script:

setenv OMP_NUM_THREADS 40

Note: Some programs ignore $OMP_NUM_THREADS and determine a number of threads programmatically.

Batch script examples

Simple sequential job

The following is an example of a single-processor sequential job that uses $TMPDIR as its working area. It assumes that the program mysci has already been built. The script copies its input file from the directory the qsub command was called from into $TMPDIR, runs the code in $TMPDIR, and copies the output files back to the original directory.

#SBATCH --account=pas1234
#SBATCH --job-name=myscience
#SBATCH --time=40:00:00
#SBATCH --ntasks=1

cd $SLURM_SUBMIT_DIR
cp mysci.in $TMPDIR
cd $TMPDIR    
/usr/bin/time ./mysci > mysci.hist
cp mysci.hist mysci.out $SLURM_SUBMIT_DIR

Serial job with OpenMP multithreading

This example uses 1 node with 40 cores, which is suitable for Pitzer. A similar job on Owens would use 28 cores; the OMP_NUM_THREADS environment variable would also be set to 28. A program must be written to take advantage of multithreading for this to work.

#SBATCH --account=pas1234
#SBATCH --job-name=my_job
#SBATCH --time=1:00:00
#SBATCH --ntasks=40
#SBATCH --constraint=40core

cd $SLURM_SUBMIT_DIR
cp a.out $TMPDIR
cd $TMPDIR
export OMP_NUM_THREADS=40
./a.out > my_results
cp my_results $SLURM_SUBMIT_DIR

Simple parallel job

Here is an example of an MPI job that uses 4 nodes with 40 cores each, running one process per core (160 processes total). This assumes a.out was built with the gnu compiler in order to illustrate the module command. The module swap command is necessary on Pitzer when running MPI programs built with a compiler other than Intel.

#SBATCH --account=pas1234
#SBATCH --job-name=my_job
#SBATCH --time=10:00:00
#SBATCH --nodes=4
#SBATCH --ntasks-per-node=40
#SBATCH --contraint=40core

module swap intel gnu
cd $SLURM_SUBMIT_DIR
pbsdcp a.out $TMPDIR
cd $TMPDIR
mpiexec a.out
pbsdcp -g 'results*' $SLURM_SUBMIT_DIR

Parallel job with MPI and OpenMP

This example is a hybrid MPI/OpenMP job. It runs one MPI process per node with 40 threads per process. The assumption here is that the code was written to support multilevel parallelism. The executable is named hybridprogram.

#SBATCH --account=pas1234
#SBATCH --job-name=my_job
#SBATCH --time=20:00:00
#SBATCH --nodes=4
#SBATCH --ntasks-per-node=40
#SBATCH --contraint=40core

export OMP_NUM_THREADS=40
export MV2_CPU_BINDING_POLICY=hybrid
cd $SLURM_SUBMIT_DIR
pbsdcp hybridprogram $TMPDIR
cd $TMPDIR
mpiexec -ppn 1 hybridprogram
pbsdcp -g 'results*' $SLURM_SUBMIT_DIR
Supercomputer: 
Service: 

Job Submission

Job scripts are submitted to the batch system using the sbatch command.  Be sure to submit your job on the system you want your job to run on.

The batch systems on different clusters are entirely separate.  You may edit your batch scripts anywhere, but you must submit and monitor your jobs from a login node on the system where you want to run.

Standard batch job

Most jobs on our system are submitted as scripts with no command-line options. If your script is in a file named myscript:

sbatch myscript

In response to this command you’ll see a line with your job ID:

Submitted batch job 123456

You’ll use this job ID (numeric part only) in monitoring your job. You can find it again using the squeue -u <username>

When you submit a job, the script is copied by the batch system. Any changes you make subsequently to the script file will not affect the job. Your input files and executables, on the other hand, are not picked up until the job starts running.

Interactive batch

The batch system supports an interactive batch mode. This mode is useful for debugging parallel programs or running a GUI program that’s too large for the login node. The resource limits (memory, CPU) for an interactive batch job are the same as the standard batch limits.

Interactive batch jobs are generally invoked without a script file, for example:

salloc --x11 --nodes=2 --ntasks-per-node=28 --time=1:00:00 srun --pty /bin/bash

The salloc command requests the resources, then srun starts an interactive shell for the requested resources. Job is interactive. The --x11 flag enables X11 forwarding, which is necessary with a GUI. You will need to have a X11 server running on your computer to use X11 forwarding, see the getting connected page. The remaining flags in this example are resource requests with the same meaning as the corresponding header lines in a batch file.

After you enter this line, you’ll see something like the following:

salloc: Pending job allocation 123456
salloc: job 123456 queued and waiting for resources

Your job will be queued just like any job. When the job runs, you’ll see the following line:

salloc: job 123456 has been allocated resources
salloc: Granted job allocation 123456
salloc: Waiting for resource configuration
salloc: Nodes o0001 are ready for job

At this point, you have an interactive login shell on one of the compute nodes, which you can treat like any other login shell.

It is important to remember that OSC systems are optimized for batch processing, not interactive computing. If the system load is high, your job may wait for hours in the queue, making interactive batch impractical. Requesting a walltime limit of one hour or less is recommended because your job can run on nodes reserved for debugging.

Job arrays

If you submit many similar jobs at the same time, you should consider using a job array. With a single sbatch command, you can submit multiple jobs that will use the same script. Each job has a unique identifier, $SLURM_ARRAY_JOB_ID, which can be used to parameterize its behavior.

Individual jobs in a job array are scheduled independently, but some job management tasks can be performed on the entire array.

To submit an array of jobs numbered from 1 to 100, all using the script sim.job:

sbatch --array=1-100 sim.job

The script would use the environment variable $SLURM_ARRAY_JOB_ID, possibly as an input argument to an application or as part of a file name.

Job dependencies

It is possible to set conditions on when a job can start. The most common of these is a dependency relationship between jobs.

For example, to ensure that the job being submitted (with script sim.job) does not start until after job 123456 has finished:

sbatch --dependency=afterany:123456 sim.job

Job variables

It is possible to provide a list of environment variables that are exported to the job. 

For example, to pass the variable and its value to the job with the script sim.job, use the command:

sbatch --export=var=value​ sim.job

Many other options are available, some quite complicated; for more information, see the sbatch online manual by using the command:

man sbatch
Supercomputer: 
Service: 

Monitoring and Managing Your Job

There are several commands available that allow you to check the status of your job, monitor execution of a running job, and collect performance statistics for your job. You can also delete a job if necessary.

Status of queued jobs

You can monitor the batch queues and check the status of your job using the command squeue. This section also addresses the question of why a job may have a long queue wait and explains a little about how job scheduling works.

squeue

Use the squeue command to check the status of your jobs. You can see whether your job is queued or running, along with information about requested resources. If the job is running you can see elapsed time and resources used.

Here are some examples for user usr1234 and job 123456.

By itself, squeue lists all jobs in the system.

To list all the jobs belonging to a particular user:

squeue -u usr1234

To list the status of a particular job, in standard or alternate (more useful!) format:

squeue -j 123456

To get more details about a particular job:

squeue -j 123456 -l

The output can also be filtered by the state of a job.

To view only running jobs use:

squeue -u usr1234 -t RUNNING

Other states can be seen in the JOB STATE CODES section of squeue man page.

There are also JOB REASON CODES mentioned in the man page, will describe why a job is pending or the nodes that the job was allocated if it is running. Use the  -l to view this information. There are several reasons a job may be pending.

  • If a user or group has reached the limit on the number of cores allowed, the rest of their jobs will be pending with a reason code of MaxCpuPerAccount.
  • If a user sets up dependencies among jobs or conditions that have to be met before a job can run, the jobs will be pending until the dependencies or conditions are met. The reason code will be Dependency.
  • You can place a hold on your own job using scontrol hold jobid.
  • If you see one of your jobs in a state that is not understood, contact OSC Help for assistance.

To list blocked jobs:

squeue -u usr1234 -t PENDING

The --start option gives an estimate for the start time of a job that is pending. Unfortunately, these estimates are not at all accurate except for the highest priority job in the queue.

Why isn’t my job running?

There are many reasons that your job may have to wait in the queue longer than you would like. Here are some of them.

  • System load is high. It’s frustrating for everyone!
  • A system downtime has been scheduled and jobs are being held. Check the message of the day, which is displayed every time you login, or the system notices posted on OSC webpage.
  • You or your group have used a lot of resources in the last few days, causing your job priority to be lowered (“fairness policy”).
  • You or your group are at the maximum processor count or running job count and your job is being held.
  • Your job is requesting specialized resources, such as large memory or certain software licences, that are in high demand.
  • Your job is requesting a lot of resources. It takes time for the resources to become available.
  • Your job is requesting incompatible or nonexistent resources and can never run.
  • Job is unnecessarily stuck in batch hold because of system problems (very rare!).

Priority, backfill, and debug reservations

Priority is a complicated function of many factors, including the processor count and walltime requested, the length of time the job has been waiting, and how much other computing has been done by the user and their group over the last several days.

During each scheduling iteration, the scheduler will identify the highest priority job that cannot currently be run and find a time in the future to reserve for it. Once that is done, the scheduler will then try to backfill as many lower priority jobs as it can without affecting the highest priority job's start time. This keeps the overall utilization of the system high while still allowing reasonable turnaround time for high priority jobs. Short jobs and jobs requesting few resources are the easiest to backfill.

A small number of nodes are set aside during the day for jobs with a walltime limit of 1 hour or less, primarily for debugging purposes.

Observing a running job

You can monitor a running batch job almost as easily as you can monitor a program running interactively. All that is needed is to view the output file in read-only mode to check the current output of the job.

node status

It may be useful to check the status of a node while the job is running. This can be done by visiting the OSC grafana page and using the 'cluster metrics' report.

Managing your jobs

Deleting a job

Situations may arise in which you want to delete one of your jobs from the SLURM queue. Perhaps you set the resource limits incorrectly, neglected to copy an input file, or had incorrect or missing commands in the batch file. Or maybe the program is taking too long to run (infinite loop).

The command to delete a batch job is scancel. It applies to both queued and running jobs.

Example:

scancel 123456

If you are unable to delete one of your jobs, it may be because of a hardware problem or system software crash. In this case you should contact OSC Help.

Altering a queued job

You can alter certain attributes of your job while it’s in the queue using the scontrol update command. This can be useful if you want to make a change without losing your place in the queue. You cannot make any alterations to the executable portion of the script, nor can you make any changes after the job starts running.

The syntax is:

scontrol update job=<jobid> <args>

The options argument consists of one or more SLURM directives in the form of command-line options.

For example, to change the walltime limit on job 123456 to 5 hours and have email sent when the job ends (only):

scontrol update job=123456 timeLimit=5:00:00 mailType=End

Placing a hold on a queued job

If you want to prevent a job from running but leave it in the queue, you can place a hold on it using the scontrol hold command. The job will remain pending until you release it with the sontrol release command. A hold can be useful if you need to modify the input file for a job, for example, but you don’t want to lose your place in the queue.

Examples:

scontrol hold 123456
scontrol release 123456

Job statistics

There are commands you can include in your batch script to collect job statistics or performance information.

A simple way to view job information is to use this command at the end of the job:

scontrol show job=$SLURM_JOB_ID

XDMoD tool

The online interactive tool XDMoD can be used to look at the usage statistics for jobs.

See XDMoD overview for more information on XDMoD.

date

The date command prints the current date and time. It can be informative to include it at the beginning and end of the executable portion of your script as a rough measure of time spent in the job.

time

The time utility is used to measure the performance of a single command. It can be used for serial or parallel processes. Add /usr/bin/time to the beginning of a command in the batch script:

/usr/bin/time myprog arg1 arg2

The result is provided in the following format:

  1. user time (CPU time spent running your program)
  2. system time (CPU time spent by your program in system calls)
  3. elapsed time (wallclock)
  4. % CPU used
  5. memory, pagefault and swap statistics
  6. I/O statistics

These results are appended to the job's error log file. Note: Use the full path “/usr/bin/time” to get all the information shown.

Scheduling Policies and Limits

The batch scheduler is configured with a number of scheduling policies to keep in mind. The policies attempt to balance the competing objectives of reasonable queue wait times and efficient system utilization. The details of these policies differ slightly on each system. Exceptions to the limits can be made under certain circumstances; contact oschelp@osc.edu for details.

Hardware limits

Each system differs in the number of processors (cores) and the amount of memory and disk they have per node. We commonly find jobs waiting in the queue that cannot be run on the system where they were submitted because their resource requests exceed the limits of the available hardware. Jobs never migrate between systems, so please pay attention to these limits.

Notice in particular the large number of standard nodes and the small number of large-memory nodes. Your jobs are likely to wait in the queue much longer for a large-memory node than for a standard node. Users often inadvertently request slightly more memory than is available on a standard node and end up waiting for one of the scarce large-memory nodes, so check your requests carefully.

This is a brief summary on Pitzer. Details about the available hardware can be found elsewhere in the documentation.

 

# of Nodes # of cores per node (ppn) Memory (*approximate)

Temporary File Space (TB)

Pitzer (standard) 224 40 198 GB 1 TB
Pitzer (hugemem) 4 80 3 TB 1 TB
         

* The actual amount of memory you can request in GB is slightly less than the nominal amount shown.

Walltime limits per job

Serial jobs (that is, jobs which request only one node) can run for up to 168 hours, while parallel jobs may run for up to 96 hours.

Users who can demonstrate a need for longer serial job time may request access to the longserial queue, which allows single-node jobs of up to 336 hours. Longserial access is not automatic. Factors that will be considered include how efficiently the jobs use OSC resources and whether they can be broken into smaller tasks that can be run separately.

Limits per user and group

These limits are applied separately on each system.

An individual user can have up to 128 concurrently running jobs and/or up to 2040  processor cores in use on Pitzer. All the users in a particular group/project can among them have up to 192 concurrently running jobs and/or up to 2040 processor cores in use on Pitzer. Jobs submitted in excess of these limits are queued but blocked by the scheduler until other jobs exit and free up resources.

A user may have no more than 1000 jobs submitted to both the parallel and serial job queue separately. Jobs submitted in excess of this limit will be rejected.

Fair-share limits

To keep any one user or group/project from monopolizing the system when others need the same resources, the scheduler imposes what are known as fair-share limits. If a user or group/project uses large amounts of computing resources over a period of a few days, any new jobs they submit during that period will have reduced priority.

Priority

The priority of a job is influenced by a large number of factors, including the processor count requested, the length of time the job has been waiting, and how much other computing has been done by the user and their group over the last several days. However, having the highest priority does not necessarily mean that a job will run immediately, as there must also be enough processors and memory available to run it.

Short jobs for debugging

A small number of nodes are set aside during the day for jobs with a walltime limit of 1 hour or less. Please remember to exit debug jobs when you are done using the resources, to free them up for other users.

GPU Jobs

All GPU nodes are reserved for jobs that request gpus. Short non-GPU jobs are allowed to backfill on these nodes to allow for better utilization of cluster resources.

Supercomputer: 

SLURM Directives Summary

SLURM directives may appear as header lines in a batch script or as options on the sbatch command line. They specify the resource requirements of your job and various other attributes. Many of the directives are discussed in more detail elsewhere in this document. The online manual page for sbatch (man sbatch) describes many of them.

SLURM header lines must come before any executable lines in your script. Their syntax is:

#SBATCH [option]

where option can be one of the options in the table below (there are others which can be found in the manual). For example, to request 4 nodes with 12 processors per node:

#SBATCH --nodes=4
#SBTACH --ntasks-per-node=40
#SBATCH --constraint=40core

The syntax for including an option on the qsub command line is:

sbatch [option]

For example, the following line submits the script myscript.job but adds the --time nodes directive:

sbatch --time=00:30:00 myscript.job
Description and examples of sbatch options
Option Description
--time=dd-hh:mm:ss

Requests the amount of time needed for the job.
Default is one hour.

--nodes=n Number of nodes to request. Default is one node.
--ntasks=m
or
--ntasks-per-node=m

Number of cores on a single node or number of tasks per requested node.
Default is a single core.

--gpus-per-node=g Number of gpus per node. Default is none.
--mem=xgb Specify the (RAM) main memory required per node.
--licenses=pkg@osc:N Request use of N licenses for package pkg.
--job-name=my_name Sets the job name, which appears in status listings and is used as the prefix in the job’s output and error log files. The job name must not contain spaces.
--mail-type=START Sets when to send mail to users when the job starts. There are other mail_type options including: END, FAIL.
--x11 Enable x11 forwarding for use of graphical applications.
--account=PEX1234 Use the specified for job resource charging.
--cluster=pitzer Explicitly enter which cluster to submit the job to.

 

Batch Environment Variable Summary

The batch system provides several environment variables that you may want to use in your job script. This section is a summary of the most useful of these variables. Many of them are discussed in more detail elsewhere in this document. The ones beginning with SLURM_ are described in the online manual page for sbatch (man sbatch).

Environment Variable Description
$TMPDIR The absolute path and name of the temporary directory created for this job on the local file system of each node
$PFSDIR The absolute path and name of the temporary directory created for this job on the parallel file system
$SLURM_SUBMIT_DIR The absolute path of the directory from which the batch script was started
$SLURM_GPUS_ON_NODE Number of GPUs allocated to the job on each node (works with --exclusive jobs).
$SLURM_ARRAY_JOB_ID Unique identifier assigned to each member of a job array
$SLURM_JOB_ID The job identifier assigned to the job by the batch system
$SLURM_JOB_NAME The job name supplied by the user

 

The following environment variables are often used in batch scripts but are not directly related to the batch system.

 

Environment Variable Description Comments
$OMP_NUM_THREADS The number of threads to be used in an OpenMP program See the discussion of OpenMP elsewhere in this document. Set in your script. Not all OpenMP programs use this value.
$MV2_ENABLE_AFFINITY Thread affinity option for MVAPICH2. Set this variable to 0 in your script if your program uses both MPI and multithreading. Not needed with MPI-1.
$HOME The absolute path of your home directory. Use this variable to avoid hard-coding your home directory path in your script.

 

Batch-Related Command Summary

This section summarizes two groups of batch-related commands: commands that are run on the login nodes to manage your jobs and commands that are run only inside a batch script. Only the most common options are described here.

Many of these commands are discussed in more detail elsewhere in this document. All have online manual pages (example: man sbatch ) unless otherwise noted.

In describing the usage of the commands we use square brackets [like this] to indicate optional arguments. The brackets are not part of the command.

Important note: The batch systems on Pitzer, Ruby, and Owens are entirely separate. Be sure to submit your jobs on a login node for the system you want them to run on. All monitoring while the job is queued or running must be done on the same system also. Your job output, of course, will be visible from both systems.

Commands for managing your jobs

These commands are typically run from a login node to manage your batch jobs. The batch systems on Pitzer and Owens are completely separate, so the commands must be run on the system where the job is to be run.

sbatch

The sbatch command is used to submit a job to the batch system.

Usage Desctiption Example
sbatch [ options ] script Submit a script for a batch job. The options list is rarely used but can augment or override the directives in the header lines of the script.   sbatch sim.job
sbatch -t array_request [ options ] jobid Submit an array of jobs sbatch -t 1-100 sim.job
sinteractive [ options ] Submit an interactive batch job sinteractive -n 4


squeue

The squeue command is used to display the status of batch jobs.

Usage Desctiption Example
squeue Display all jobs currently in the batch system. squeue
squeue -j jobid Display information about job jobid. The -j flag uses an alternate format. squeue -j 123456
squeue -j jobid -l Display long status information about job jobid. squeue -j 123456 -l
squeue -u username [-l] Display information about all the jobs belonging to user username. squeue -u usr1234

scancel

The scancel command may be used to delete a queued or running job.

Usage Description Example
scancel jobid Delete job jobid.

scancel 123456

scancel jobid Delete all jobs in job array jobid. scancel 123456
qdel jobid[jobnumber] Delete jobnumber within job array jobid. scancel 123456_14

slurm output file

There is an output file which stores the stdout and stderr for a running job which can be viewed to check the running job output. It is by default located in the dir where the job was submitted and has the format:

slurm-<jobid>.out
Do not delete/modify the output file that is generated while your job running. This could cause adverse affects on your running job.

scontrol

The scontrol command may be used to modify the attributes of a queued (not running) job. Not all attributes can be altered.

Usage Description Example
scontrol update jobid=<jobid> [ option ] Alter one or more attributes a queued job. The options you can modify are a subset of the directives that can be used when submitting a job.

scontrol update jobid=123456 --ntasks=4

scontrol hold/release

The qhold command allows you to place a hold on a queued job. The job will be prevented from running until you release the hold with the qrls command.

Usage Description Example
scontrol hold jobid Place a user hold on job jobid scontrol hold 123456
scontrol release jobid Release a user hold previously placed on job jobid scontrol release 123456

estimating start time

The squeue command can try to estimate when a queued job will start running. It is extremely unreliable, often making large errors in either direction.

Usage Description Example
squeue -j jobid \
--Format=username,jobid,account,startTime
Display estimate of start time.
squeue -j 123456 \ 
--Format=username,jobid,account,startTime

 

Commands used only inside a batch job

 

These commands can only be used inside a batch job.

mpiexec

Use the mpiexec command to run a parallel program or to run multiple processes simultaneously within a job. It is a replacement program for the script mpirun , which is part of the mpich package.
The OSC version of mpiexec is customized to work with our batch environment. There are other mpiexec programs in existence, but it is imperative that you use the one provided with our system.

Usage Description Example
mpiexec progname [ args ] Run the executable program progname in parallel, with as many processes as there are processors (cores) assigned to the job (nodes*ppn).

mpiexec myprog

mpiexec yourprog abc.dat 123

mpiexec - ppn 1 progname [ args ] Run only one process per node. mpiexec -ppn 1 myprog
mpiexec - ppn num progname [ args ] Run the specified number of processes on each node. mpiexec -ppn 3 myprog
mpiexec -tv [ options ] progname [ args ] Run the program with the TotalView parallel debugger.

mpiexec -tv myprog

mpiexec -n num progname [ args ]

mpiexec -np num progname [ args ] Run only the specified number of processes. ( -n and -np are equivalent.) Does not spread processes out evenly across nodes. mpiexec -n 3 myprog
The options above apply to the MVAPICH2 and IntelMPI installations at OSC. See the OpenMPI software page for mpiexec usage with OpenMPI.

pbsdcp

The pbsdcp command is a distributed copy command for the SLURM environment. It copies files to or from each node of the cluster assigned to your job. This is needed when copying files to directories which are not shared between nodes, such as $TMPDIR.

Options are -r for recursive and -p to preserve modification times and modes.

Usage Description Example
pbsdcp [-s] [ options ] srcfiles  target “Scatter”. Copy one or more files from shared storage to the target directory on each node (local storage). The -s flag is optional.

pbsdcp -s infile1 infile2 $TMPDIR

pbsdcp model.* $TMPDIR

pbsdcp -g [ options ] srcfiles  target “Gather”. Copy the source files from each node to the shared target directory. Wildcards must be enclosed in quotes. pbsdcp -g '$TMPDIR/outfile*' $PBS_O_WORKDIR

Note: In gather mode, if files on different nodes have the same name, they will overwrite each other. In the -g example above, the file names may have the form outfile001 , outfile002 , etc., with each node producing a different set of files.

end of job accounting info

To view the overall statistics of a job, at the end use the command:

scontrol show job=$SLURM_JOB_ID

 

Messages from sbatch

sbatch messages

shell warning

Submitting a job without specifying the proper shell will return a warning like below:

sbatch: WARNING: Job script lacks first line beginning with #! shell. Injecting '#!/bin/bash' as first line of job script.

Errors

If an error is encountered, the job is rejected.

Not specifying a project account

It is required for to specify an account for a job to run. Please use the --account=<project-code> option to do this.

sbatch: error: ERROR: Job invalid: Must specify account for job
sbatch: error: Job submit/allocate failed: Unspecified error

Specify wrong account

If a user tries to set the --account option with a project that they are not on, then the job is rejected.

sbatch: error: Job submit/allocate failed: Invalid account or account/partition combination specified

Using a restricted project in a slurm job

If a user submits a job and uses a project that is restricted, the following message will be shown and the job will not be submitted:

sbatch: error: AssocGrpSubmitJobsLimit
sbatch: error: Batch job submission failed: Job violates accounting/QOS policy (job submit limit, user's size and/or time limits)

Leading whitespace in job name

Leading whitespace is not supported in SLURM job names. Your job will be rejected with an error message if you submit a job with a space in the job name:

sbatch: error: Invalid directive found in batch script: name

You can fix this by removing leading whitespace in the job name.

Script is empty or only contains whitespace

An empty file is not permitted to be submitted (included whitespace only files).

sbatch: error: Batch script is empty!

or

sbatch: error: Batch script contains only whitespace!

 

Supercomputer: 
Service: 

Troubleshooting Batch Problems

License problems

If you get a license error when you try to run a third-party software application, it means either the licenses are all in use or you’re not on the access list for the license. Very rarely there could be a problem with the license server. You should read the software page for the application you’re trying to use and make sure you’ve complied with all the procedures and are correctly requesting the license. Contact OSC Help with any questions.

My job is running slower than it should

Here are a few of the reasons your job may be running slowly:

  • Your job has exceeded available physical memory and is swapping to disk. This is always a bad thing in an HPC environment as it can slow down your job dramatically. Either cut down on memory usage, request more memory, or spread a parallel job out over more nodes.
  • Your job isn’t using all the nodes and/or cores you intended it to use. This is usually a problem with your batch script.
  • Your job is spawning more threads than the number of cores you requested. Context switching involves enough overhead to slow your job.
  • You are doing too much I/O to the network file servers (home and project directories), or you are doing an excessive number of small I/O operations to the parallel file server. An I/O-bound program will suffer severe slowdowns with improperly configured I/O.
  • You didn’t optimize your program sufficiently.
  • You got unlucky and are being hurt by someone else’s misbehaving job. As much as we try to isolate jobs from each other, sometimes a job can cause system-level problems. If you have run your job before and know that it usually runs faster, OSC staff can check for problems.

Someone deleted my job!

If your job is misbehaving, it may be necessary for OSC staff to delete it. Common problems are using up all the virtual memory on a node or performing excessive I/O to a network file server. If this happens you will be contacted by OSC Help with an explanation of the problem and suggestions for fixing it. We appreciate your cooperation in this situation because, much as we try to prevent it, one user’s jobs can interfere with the operation of the system.

Occasionally a problem not caused by your job will cause an unrecoverable situation and your job will have to be deleted. You will be contacted if this happens.

Why can’t I delete my job?

If you can’t delete your job, it usually means a node your job was running on has crashed and the job is no longer running. OSC staff will delete the job.

My job is stuck.

There are multiple reasons that your job may appear to be stuck. If a node that your job is running on crashes, your job may remain in the running job queue long after it should have finished. In this case you will be contacted by OSC and will probably have to resubmit your job.

If you conclude that your job is stuck based on what you see in the slurm output file, it’s possible that the problem is an illusion. This comment applies primarily to code you develop yourself. If you print progress information, for example, “Input complete” and “Setup complete”, the output may be buffered for efficiency, meaning it’s not written to disk immediately, so it won’t show up. To have it written immediate, you’ll have to flush the buffer; most programming languages provide a way to do this.

My job crashed. Can I recover my data?

If your job failed due to a hardware failure or system problem, it may be possible to recover your data from $TMPDIR. If the failure was due to hitting the walltime limit, the data in $TMPDIR would have been deleted immediately. Contact OSC Help for more information.

The trap command can be used in your script to save your data in case your job terminates abnormally.

Contacting OSC Help

If you are having a problem with the batch system on any of OSC's machines, you should send email to oschelp@osc.edu. Including the following information will assist HPC Client Services staff in diagnosing your problem quickly:

  1. Name
  2. OSC User ID (username)
  3. Name of the system you are using (Oakley, Ruby, or Owens)
  4. Job ID
  5. Job script
  6. Job output and/or error messages (preferably in context)

Or use the support request page.

batch email notifications

Occasionally, jobs that experience problems may generate emails from staff or automated systems at the center with some information about the nature of the problem. This page provides additional information about the various emails sent, and steps that can be taken to address the problem.

batch emails

All emails from osc about jobs will come from slurm@osc.edu, oschelp@osc.edu, or an email address with the domain @osc.edu

regular job emails

These emails can be turned on/off using the appropriate slurm directives. Other email addresses can also be specified. See the mail options section of job scripts page.

Email type Description
job began/end Job began or ended. These are normal emails.
job aborted Job has ended in an abnormal state.

other emails

There is no option to turn these emails off, as they require us to contact the user that submitted the job. We can work with you if they will be expected. Please contact OSC Help in this case.

Email type Description
Deleted by administrator

OSC staff may delete running jobs if:

  • The job is using so much memory that it threatens to crash the node it is running on.
  • The job is using more resources than it requested and is interfering with other jobs running on the same node.
  • The job is causing excessive load on some part of the system, typically a network file server.
  • The job is still running at the start of a scheduled downtime.

OSC staff may delete queued jobs if:

  • The job requests non-existent resources.
  • A job intended for one system that was submitted on another one.
  • The job can never run because it requests combinations of resources that are disallowed by policy.
  • The user’s credentials are blocked on the system the job was submitted on.
Emails exceed expected volume Job emails may be delayed if too many are queued to be sent to a single email address. This is to prevent OSC from being blacklisted by the email server.
failure due to hardware/software problem The node(s) or software that a job was using had a critical issue and the job failed.
overuse of physical memory (RAM)

The node that was in use crashed due to it being out of memory.

See out-of-memory (OOM) or excessive memory usage page for more information.

Job requeued A job may be requeued explicitly by a system administrator or after a node failure.
GPFS unmount

An issue with gpfs may have affected the job. This includes directories located in:

  • /fs/ess
  • /fs/project
  • /fs/scratch.
Filling up /tmp Job failed after exhausting the space in a node's local /tmp directory.

For assistance

Contact OSC Help for assistance if there are any questions.

 

Slurm Migration

Overview

Slurm, which stands for Simple Linux Utility for Resource Management, is a widely used open-source HPC resource management and scheduling system that originated at Lawrence Livermore National Laboratory.

It is decided that OSC will be implementing Slurm for job scheduling and resource management, to replace the Torque resource manager and Moab scheduling system that it currently uses, over the course of 2020.

Phases of Slurm Migration

It is expected that on Jan 1, 2021, both Pitzer and Owens clusters will be using Slurm. OSC will be switching to Slurm on Pitzer with the deployment of the new Pitzer hardware in September 2020. Owens migration to Slurm will occur later this fall.

PBS Compatibility Layer

During Slurm migration, OSC enables PBS compatibility layer provided by Slurm in order to make the transition as smooth as possible. Therefore, PBS batch scripts that used to work in the previous Torque/Moab environment mostly still work in Slurm. However, we encourage you to start to convert your PBS batch scripts to Slurm scripts because

  • PBS compatibility layer usually handles basic cases, and may not be able to handle some complicated cases 
  • Slurm has many features that are not available in Moab/Torque, and the layer will not provide access to those features
  • OSC may turn off the PBS compatibility layer in the future

Please check the following pages on how to submit a Slurm job:

Further Reading

Supercomputer: 
Service: 

How to Prepare Slurm Job Scripts

As the first step, you can submit your PBS batch script as you did before to see whether it works or not. If it does not work, you can either follow this page for step-by-step instructions, or read the tables below to convert your PBS script to Slurm script by yourself. Once the job script is prepared, you can refer to this page to submit and manage your jobs.

Job Submission Options

Use Torque/Moab Slurm Equivalent
Script directive #PBS #SBATCH
Job name -N <name> --job-name=<name>
Project account -A <account> --account=<account>
Queue or partition -q queuename --partition=queuename

Wall time limit

-l walltime=hh:mm:ss --time=hh:mm:ss
Node count -l nodes=N --nodes=N
Process count per node -l ppn=M --ntasks-per-node=M
Memory limit -l mem=Xgb --mem=Xgb (it is MB by default)
Request GPUs -l nodes=N:ppn=M:gpus=G --nodes=N --ntasks-per-node=M --gpus-per-node=G
Request GPUs in default mode -l nodes=N:ppn=M:gpus=G:default

--nodes=N --ntasks-per-node=M --gpus-per-node=G --gpu_cmode=shared

Require pfsdir or ime -l nodes=N:ppn=M:[pfsdir or ime] --nodes=N --ntasks-per-node=M --gres=[pfsdir or ime]
Require 'vis'  -l nodes=N:ppn=M:gpus=G:vis --nodes=N --ntasks-per-node=M --gpus-per-node=G --gres=vis

Require special property

-l nodes=N:ppn=M:property --nodes=N --ntasks-per-node=M --constraint=property

Job array

-t <array indexes> --array=<indexes>

Standard output file

-o <file path> --output=<file path>/<file name> (path must exist, and you must specify the name of the file)

Standard error file

-e <file path> --error=<file path>/<file name> (path must exist, and you must specify the name of the file)

Job dependency

-W depend=after:jobID[:jobID...]

-W depend=afterok:jobID[:jobID...]

-W depend=afternotok:jobID[:jobID...]

-W depend=afterany:jobID[:jobID...]

--dependency=after:jobID[:jobID...]

--dependency=afterok:jobID[:jobID...]

--dependency=afternotok:jobID[:jobID...]

--dependency=afterany:jobID[:jobID...]

Request event notification -m <events>

--mail-type=<events>

Note: multiple mail-type requests may be specified in a comma-separated list:

--mail-type=BEGIN,END,NONE,FAIL,ALL

Email address -M <email address> --mail-user=<email address>
Software flag -l software=pkg1+1%pkg2+4 --licenses=pkg1@osc:1,pkg2@osc:4
Require reservation -l advres=rsvid --reservation=rsvid

Job Environment Variables

Info Torque/Moab Environment Variable Slurm Equivalent
Job ID $PBS_JOBID $SLURM_JOB_ID
Job name $PBS_JOBNAME $SLURM_JOB_NAME
Queue name $PBS_QUEUE $SLURM_JOB_PARTITION
Submit directory $PBS_O_WORKDIR $SLURM_SUBMIT_DIR
Node file cat $PBS_NODEFILE srun hostname |sort -n
Number of processes $PBS_NP $SLURM_NTASKS
Number of nodes allocated $PBS_NUM_NODES $SLURM_JOB_NUM_NODES
Number of processes per node $PBS_NUM_PPN $SLURM_TASKS_PER_NODE
Walltime $PBS_WALLTIME $SLURM_TIME_LIMIT
Job array ID $PBS_ARRAYID $SLURM_ARRAY_JOB_ID
Job array index $PBS_ARRAY_INDEX $SLURM_ARRAY_TASK_ID

Environment Variables Specific to OSC

Environment variable Description
$TMPDIR Path to a node-specific temporary directory (/tmp) for a given job
$PFSDIR Path to the scratch storage; only present if --gres request includes pfsdir.
$IMEDIR Path to IME for PFSDIR; only present if --gres=pfsdir,ime or --gres=pfsdir:scratch,ime
$SLURM_GPUS_ON_NODE Number of GPUs allocated to the job on each node (works with --exclusive jobs)
$SLURM_JOB_GRES The job's GRES request
$SLURM_JOB_CONSTRAINT The job's constraint request
$SLURM_TIME_LIMIT Job walltime in seconds

Commands in a Batch Job

Use Torque/Moab Environment Variable Slurm Equivalent
Launch a parallel program inside a job mpiexec <args> srun <args>
Scatter a file to node-local file systems pbsdcp <file> <nodelocaldir> sbcast <src_file> <nodelocaldir>/<dest_file>
Gather node-local files to a shared file system pbsdcp -g <file> <shareddir>

sgather <src_file> <shareddir>/<dest_file>
 sgather -r <src_dir> <sharedir>/dest_dir>

Supercomputer: 

How to Submit, Monitor and Manage Jobs

Submit Jobs

Use Torque/Moab Command Slurm Equivalent
Submit batch job qsub <jobscript> sbatch <jobscript>
Submit interactive job qsub -I [options]

sinteractive [options]

salloc [options]

Interactive jobs

Submitting interactive jobs is a bit different in Slurm. When the job is ready, one is logged into the login node they submitted the job from. From there, one can then login to one of the reserved nodes.

You can use the custom tool sinteractive as:

[xwang@pitzer-login04 ~]$ sinteractive
salloc: Pending job allocation 14269
salloc: job 14269 queued and waiting for resources
salloc: job 14269 has been allocated resources
salloc: Granted job allocation 14269
salloc: Waiting for resource configuration
salloc: Nodes p0591 are ready for job
...
...
[xwang@p0593 ~] $
# can now start executing commands interactively

Or, you can use salloc as:

[user@pitzer-login04 ~] $ salloc -t 00:05:00 --ntasks-per-node=3
salloc: Pending job allocation 14209
salloc: job 14209 queued and waiting for resources
salloc: job 14209 has been allocated resources
salloc: Granted job allocation 14209
salloc: Waiting for resource configuration
salloc: Nodes p0593 are ready for job

# normal login display
$ squeue
JOBID PARTITION     NAME     USER ST       TIME  NODES NODELIST(REASON)
14210 serial-48     bash     usee  R       0:06      1 p0593
[user@pitzer-login04 ~]$ srun --jobid=14210 --pty /bin/bash
# normal login display
[user@p0593 ~] $
# can now start executing commands interactively

Manage Jobs

Use Torque/Moab Command Slurm Equivalent
Delete a job qdel <jobid>  scancel <jobid>
Hold a job qhold <jobid> scontrol hold <jobid>
Release a job qrls <jobid>  scontrol release <jobid>

Monitor Jobs

Use Torque/Moab Command Slurm Equivalent
Job list summary qstat or showq squeue
Detailed job information qstat -f <jobid> or checkjob <jobid> sstat -j <jobid> or scontrol show job <jobid>
Job information by a user qstat -u <user> squeue -u <user>

View job script

(system admin only)

js <jobid> jobscript <jobid>
Show expected start time showstart <job ID> squeue --start --jobs=<jobid>
Supercomputer: 

Steps on How to Submit Jobs

How to Submit Interactive jobs

There are different ways to submit interactive jobs.

Using qsub

qsub command is patched locally to handle the interactive jobs. So mostly you can use the qsub command as before:

[xwang@pitzer-login04 ~]$ qsub -I -l nodes=1 -A PZS0712
salloc: Pending job allocation 15387
salloc: job 15387 queued and waiting for resources
salloc: job 15387 has been allocated resources
salloc: Granted job allocation 15387
salloc: Waiting for resource configuration
salloc: Nodes p0601 are ready for job
...
[xwang@p0601 ~]$ 
# can now start executing commands interactively

Using sinteractive

You can use the custom tool sinteractive as:

[xwang@pitzer-login04 ~]$ sinteractive
salloc: Pending job allocation 14269
salloc: job 14269 queued and waiting for resources
salloc: job 14269 has been allocated resources
salloc: Granted job allocation 14269
salloc: Waiting for resource configuration
salloc: Nodes p0591 are ready for job
...
...
[xwang@p0593 ~] $
# can now start executing commands interactively

Using salloc

It is a little complicated if you use salloc . Below is a simple example:

[user@pitzer-login04 ~] $ salloc -t 00:30:00 --ntasks-per-node=3 srun --pty /bin/bash
salloc: Pending job allocation 2337639
salloc: job 2337639 queued and waiting for resources
salloc: job 2337639 has been allocated resources
salloc: Granted job allocation 2337639
salloc: Waiting for resource configuration
salloc: Nodes p0002 are ready for job

# normal login display
[user@p0002 ~]$
# can now start executing commands interactively

How to Submit Non-interactive jobs

Submit PBS job Script

Since we have the compatibility layer installed, your current PBS scripts may still work as they are, so you should test them and see if they submit and run successfully. Submit your PBS batch script as you did before to see whether it works or not. Below is a simple PBS job script pbs_job.txt that calls for a parallel run:

#PBS -l walltime=1:00:00
#PBS -l nodes=2:ppn=40
#PBS -N hello
#PBS -A PZS0712

cd $PBS_O_WORKDIR
module load intel
mpicc -O2 hello.c -o hello
mpiexec ./hello > hello_results

Submit this script on Pitzer using the command qsub pbs_job.txt , and this job is scheduled successfully as shown below:

[xwang@pitzer-login04 slurm]$ qsub pbs_job.txt 
14177

Check the Job

You can use the jobscript command to check the job information:

[xwang@pitzer-login04 slurm]$ jobscript 14177
-------------------- BEGIN jobid=14177 --------------------
#!/bin/bash
#PBS -l walltime=1:00:00
#PBS -l nodes=2:ppn=40
#PBS -N hello
#PBS -A PZS0712

cd $PBS_O_WORKDIR
module load intel
mpicc -O2 hello.c -o hello
mpiexec ./hello > hello_results

-------------------- END jobid=14177 --------------------
Please note that there is an extra line #!/bin/bash added at the beginning of the job script from the output. This line is added by Slurm's qsub compatibility script because Slurm job scripts must have #!<SHELL> as its first line.

You will get this message explicitly if you submit the script using the command sbatch pbs_job.txt

[xwang@pitzer-login04 slurm]$ sbatch pbs_job.txt 
sbatch: WARNING: Job script lacks first line beginning with #! shell. Injecting '#!/bin/bash' as first line of job script.
Submitted batch job 14180

Alternative Way: Convert PBS Script to Slurm Script

An alternative way is that we convert the PBS job script (pbs_job.txt) to Slurm script (slurm_job.txt) before submitting the job. The table below shows the comparisons between the two scripts (see this page for more information on the job submission options):

Explanations Torque Slurm
Line that specifies the shell No need
#!/bin/bash
Resource specification

 

#PBS -l walltime=1:00:00
#PBS -l nodes=2:ppn=40
#PBS -N hello
#PBS -A PZS0712
#SBATCH --time=1:00:00
#SBATCH --nodes=2 --ntasks-per-node=40
#SBATCH --job-name=hello
#SBATCH --account=PZS0712
Variables, paths, and modules
cd $PBS_O_WORKDIR
module load intel
cd $SLURM_SUBMIT_DIR 
module load intel
Launch and run application
mpicc -O2 hello.c -o hello
mpiexec ./hello > hello_results
mpicc -O2 hello.c -o hello
srun ./hello > hello_results
In this example, the line cd $SLURM_SUBMIT_DIR can be omitted in the Slurm script because your Slurm job always starts in your submission directory, which is different from Torque/Moab environment where your job always starts in your home directory.

Once the script is ready, you submit the script using the command sbatch slurm_job.txt

[xwang@pitzer-login04 slurm]$ sbatch slurm_job.txt 
Submitted batch job 14215
Supercomputer: 

Slurm Migration Issues

This page documents the known issues for migrating jobs from Torque to Slurm.

$PBS_NODEFILE and $SLURM_JOB_NODELIST

Please be aware that $PBS_NODEFILE is a file while $SLURM_JOB_NODELIST is a string variable. 

The analog on Slurm to cat $PBS_NODEFILE is srun hostname | sort -n 

Environmental variables can't be passed in the job script

The job script job.txt including  #SBATCH --output=$HOME/jobtest.out won't work in Slurm. Please use the following instead:

sbatch --output=$HOME/jobtest.out job.txt 

Using mpiexec with Intel MPI

Intel MPI on Pitzer is configured to support PMI and Hydra process managers. It is recommended to use srun as MPI program launcher. If you prefer using mpiexec on Pitzer, you might experience MPI init error or see the message:

MPI startup(): Warning: I_MPI_PMI_LIBRARY will be ignored since the hydra process manager was found

Please set unset I_MPI_PMI_LIBRARY in job before running MPI programs to resolve the issue.

Using --ntasks-per-node and --mem options together

Right now jobs using --ntasks-per-node and --mem are running into a bug where if --mem divided by MaxMemPerCPU is greater than ntasks-per-node, the job is not seen as schedulable on the partition where the MaxMemPerCPU issue exists.  The MaxMemPerCPU value is set on all partitions to be usable memory divided by cores a given type of node has.  One issue we’ve observed is jobs questing 1 GPU with --ntasks-per-node=4 and --mem=32G are incorrectly only running on the quad GPU nodes even when other GPU nodes are available.

Executables with a certain MPI library using SLURM PMI2 interface

e.g.

Stopping mpi4py python processes during an interactive job session only from a login node:

$ salloc -t 15:00 --ntasks-per-node=4
salloc: Pending job allocation 20822
salloc: job 20822 queued and waiting for resources
salloc: job 20822 has been allocated resources
salloc: Granted job allocation 20822
salloc: Waiting for resource configuration
salloc: Nodes p0511 are ready for job
# don't login to one of the allocated nodes, stay on the login node
$ module load python/3.7-2019.10
$ source activate testing
(testing) $ srun --quit-on-interrupt python mpi4py-test.py
# enter <ctrl-c>
^Csrun: sending Ctrl-C to job 20822.5
Hello World (from process 0)
process 0 is sleeping...
Hello World (from process 2)
process 2 is sleeping...
Hello World (from process 3)
process 3 is sleeping...
Hello World (from process 1)
process 1 is sleeping...
Traceback (most recent call last):
File "mpi4py-test.py", line 16, in <module>
time.sleep(15)
KeyboardInterrupt
Traceback (most recent call last):
File "mpi4py-test.py", line 16, in <module>
time.sleep(15)
KeyboardInterrupt
Traceback (most recent call last):
File "mpi4py-test.py", line 16, in <module>
time.sleep(15)
KeyboardInterrupt
Traceback (most recent call last):
File "mpi4py-test.py", line 16, in <module>
time.sleep(15)
KeyboardInterrupt
srun: Job step aborted: Waiting up to 32 seconds for job step to finish.
slurmstepd: error: *** STEP 20822.5 ON p0511 CANCELLED AT 2020-09-04T10:13:44 ***
# still in the job and able to restart the processes
(testing)

pbsdcp with Slurm

pbsdcp works correctly with Slurm. But, when you use the wildcard, it should be without quotation marks. In Torque/Moab, you can use it, for example

pbsdcp -g '*' {dest_dir} 

But, with Slurm, it should be without quotation marks:

pbsdcp -g * {dest_dir} 

If you like, you can use sbcast and/or sgather instead of pbsdcp as well.

Signal handling in slurm

The below script needs to use a wait command for the user-defined signal USR1 to be received by the process.

The sleep process is backgrounded using & wait so that the bash shell can receive signals and execute the trap commands instead of ignoring the signals while the sleep process is running.

-----
#!/bin/bash
#SBATCH --job-name=minimal_trap
#SBATCH --time=2:00
#SBATCH --nodes=1 --ntasks-per-node=1
#SBATCH --output=%x.%A.log
#SBATCH --signal=B:USR1@60

function my_handler() {
  echo "Catching signal"
  touch $SLURM_SUBMIT_DIR/job_${SLURM_JOB_ID}_caught_signal
  exit
}

trap my_handler USR1
trap my_handler TERM

sleep 3600 &
wait
-----

reference: https://bugs.schedmd.com/show_bug.cgi?id=9715

'mail' does not work; use 'sendmail'

The 'mail' does not work in a batch job; use 'sendmail' instead as:

sendmail user@example.com <<EOF
subject: Output path from $SLURM_JOB_ID
from: user@example.com
...
EOF

Please submit any issue using the webform below:

 

 
 
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Please report the problem here when you use Slurm

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Supercomputer: 

Knowledge Base

This knowledge base is a collection of important, useful information about OSC systems that does not fit into a guide or tutorial, and is too long to be answered in a simple FAQ.

Account Consolidation Guide

Initial account consolidation took place during the July 17th, 2018 downtime
Please contact OSC Help if you need further information. 

Single Account / Multiple Projects

If you work with several research groups, you had a separate account for each group. This meant multiple home directories, multiple passwords, etc. Over the years there have been requests for a single login system. We've now put that in place.

How will this affect you?

If you work with multiple groups, you'll need to be aware of how this works.

  • It will be very important to use the correct project code for batch job charging.
  • Managing the sharing of files between your projects (groups) is a little more complicated.
  • In most cases, you will only need to fill out software license agreements once.

The single username 

We requested those with multiple accounts to choose a preferred username. If one was not selected by the user, we selected one for them. 

The preferred username will be your only active account; you will not be able to log in or submit jobs with the other accounts. 

Checking the groups of a username

To check all groups of a username (USERID), use the command:

groups USERID

or

OSCfinger USERID

The first one from the output is your primary group, which is the project code (PROJECTID) this username (USERID) was created under.

All project codes your user account is under is determined by the groups displayed. One can also use the OSC Client Portal to look at their current projects.

A user may not be a member of the project, even though the user is still in the group for that project. This is because a primary group will not be removed when a user is removed from their first project. OSCfinger will list a primary group and project groups separately (if a user the primary group, but the project is not listed in the 'groups' sectionm then they are not in that project). OSC Client portal will also show current project members.

Changing the primary group for a login session

You can change the primary group of your username (USERID) to any UNIX group (GROUP) that username (USERID) belongs to during the login session using the command:

newgrp GROUP

This change is only valid during this login session. If you log out and log back in, your primary group is changed back to the default one.

Check previous user accounts

There is no available tool to check all of your previous active accounts. We sent an email to each impacted user providing the information on your preferred username and previous accounts. Please refer to that email (sent on July 11, subject "Multiple OSC Accounts - Your Single Username").

Batch job

How to specify the charging project

It will be very important that you make sure a batch job is charged against the correct research project code.

Specify a project to charge the job to using the -A flag. e.g. The following example will charge to project PAS1234.

#SBATCH -A PAS1234

Batch limits policy

The job limit per user remains the same. That is to say, though your jobs are charged against different project codes, the total number of jobs and cores your user account can use on each system is still restricted by the previous user-based limit. Therefore, consolidating multiple user accounts into one preferred user account may affect the work of some users.

Please check our batch limit policy on each system for more details.

Data Management

Managing multiple home directories

Data from your non-preferred accounts will remain in those home directories; the ownership of the files will be updated to your preferred username, the newly consolidated account. You can access your other home directories using the command cd /absolute/path/to/file

You will need to consolidate all files to your preferred username as soon as possible because we plan to purge the data in future. Please contact OSC Help if you need the information on your other home directories to access the files.  

Previous files associated with your other usernames

  • Files associated with your non-preferred accounts will have their ownership changed to your preferred username. 
  • These files won't count against your home directory file quota. 
  • There will be no change to files and quotas on the project and scratch file systems.

Change group of a file

Log in with preferred username (P_ USERID) and create a new file of which the owner and group is your preferred username (P_ USERID) and primary project code (P_PROJECTID). Then change the group of the newly created file (FILE) using the command:

chgrp PROJECTID FILE

Managing file sharing in a batch job

In the Linux file system, every file has an owner and a group. By default, the group (project code) assigned to a file is the primary group of the user who creates it. This means that even if you change the charged account for a batch job, any files created will still be associated with your primary group.

To change the group for new files you will need to update your primary group prior to submitting your slurm script using the newgrp command.

It is important to remember that groups are used in two different ways: for resource use charging and file permissions. In the simplest case, if you are a member of only one research group/project, you won't need either option above. If you are in multiple research groups and/or multiple projects, you may need something like:

newgrp PAS0002
sbatch -A PAS0002 myjob.sh

OnDemand users

If you use the OnDemand Files app to upload files to the OSC filesystem, the group ownership of uploaded files will be your primary group.

Software licenses

  • We will merge all your current agreements if you have multiple accounts.  
  • In many cases, you will only need to fill out software license agreements once.
  • Some vendors may require you to sign an updated agreement.  
  • Some vendors may also require the PI of each of your research groups/project codes to sign an agreement.
Supercomputer: 

Changes of Default Memory Limits

Problem Description

Our current GPFS file system is a distributed process with significant interactions between the clients. As the compute nodes being GPFS flle system clients, a certain amount of memory of each node needs to be reserved for these interactions. As a result, the maximum physical memory of each node allowed to be used by users' jobs is reduced, in order to keep the healthy performance of the file system. In addition, using swap memory is not allowed.  

The table below summarizes the maximum physical memory allowed for each type of nodes on our systems:

Owens Cluster

NODE TYPE PHYSICAL MEMORY per node MAXIMUM MEMORY ALLOWED per node
Regular node 128GB 118GB
Huge memory node 1536GB (1.5TB)

1493GB

Pitzer Cluster

Node type physical memory per node Maximum memory allowed per Node 
Regular node 192GB 178GB
Dual GPU node 384GB 363GB
Quad GPU node 768 GB 744 GB
Large memory node 768 GB 744 GB
Huge memory node 3072GB (3TB) 2989GB

Solutions When You Need Regular Nodes

If you do not request memory explicitly in your job (no --mem

Your job can be submitted and scheduled as before, and resources will be allocated according to your requests for cores/nodes ( --nodes=XX --ntask=XX ).  If you request a partial node, the memory allocated to your job is proportional to the number of cores requested; if you request the whole node, the memory allocated to your job is based on the information summarized in the above tables.

If you have a multi-node job (  nodes>1  ), your job will be assigned the entire nodes with maximum memory allowed per node and charged for the entire nodes regardless of --ntask request.

If you do request memory explicitly in your job (with  --mem 

If you request memory explicitly in your script, please re-visit your script according to the following pages:

Pitzer: https://www.osc.edu/resources/technical_support/supercomputers/pitzer/batch_limit_rules 

Owens: https://www.osc.edu/resources/technical_support/supercomputers/owens/batch_limit_rules 

Supercomputer: 
Service: 

Compilation Guide

As a general recommendation, we suggest selecting the newest compilers available for a new project. For repeatability, you may not want to change compilers in the middle of an experiment.

Pitzer Compilers

The Skylake processors that make up Pitzer support the AVX512 instruction set, but you must set the correct compiler flags to take advantage of it. AVX512 has the potential to speed up your code by a factor of 8 or more, depending on the compiler and options you would otherwise use.

With the Intel compilers, use -xHost and -O2 or higher. With the gnu compilers, use -march=native and -O3. The PGI compilers by default use the highest available instruction set, so no additional flags are necessary.

This advice assumes that you are building and running your code on Pitzer. The executables will not be portable.  Of course, any highly optimized builds, such as those employing the options above, should be thoroughly validated for correctness.

Intel (recommended)

  NON-MPI MPI
FORTRAN 90 ifort mpif90
C icc mpicc
C++ icpc mpicxx

Recommended Optimization Options

The   -O2 -xHost  options are recommended with the Intel compilers. (For more options, see the "man" pages for the compilers.

OpenMP

Add this flag to any of the above:  -qopenmp  

PGI

  NON-MPI MPI
FORTRAN 90 pgfortran   or   pgf90 mpif90
C pgcc mpicc
C++ pgc++ mpicxx

Recommended Optimization Options

The   -fast  option is appropriate with all PGI compilers. (For more options, see the "man" pages for the compilers)

Note: The PGI compilers can generate code for accelerators such as GPUs. Description of these capabilities is beyond the scope of this guide.

OpenMP

Add this flag to any of the above:  -mp

GNU

  NON-MPI MPI
FORTRAN 90 gfortran mpif90
C gcc mpicc
C++ g++ mpicxx

Recommended Optimization Options

The  -O2 -march=native  options are recommended with the GNU compilers. (For more options, see the "man" pages for the compilers)

OpenMP

Add this flag to any of the above:  -fopenmp

 

Owens Compilers

The Haswell and Broadwell processors that make up Owens support the Advanced Vector Extensions (AVX2) instruction set, but you must set the correct compiler flags to take advantage of it. AVX2 has the potential to speed up your code by a factor of 4 or more, depending on the compiler and options you would otherwise use.

With the Intel compilers, use -xHost and -O2 or higher. With the gnu compilers, use -march=native and -O3. The PGI compilers by default use the highest available instruction set, so no additional flags are necessary.

This advice assumes that you are building and running your code on Owens. The executables will not be portable. Of course, any highly optimized builds, such as those employing the options above, should be thoroughly validated for correctness.

Intel (recommended)

  NON-MPI MPI
FORTRAN 90 ifort mpif90
C icc mpicc
C++ icpc mpicxx

Recommended Optimization Options

The   -O2 -xHost  options are recommended with the Intel compilers. (For more options, see the "man" pages for the compilers.

OpenMP

Add this flag to any of the above:  -qopenmp  or  -openmp

PGI

  NON-MPI MPI
FORTRAN 90 pgfortran   or   pgf90 mpif90
C pgcc mpicc
C++ pgc++ mpicxx

Recommended Optimization Options

The   -fast  option is appropriate with all PGI compilers. (For more options, see the "man" pages for the compilers)

Note: The PGI compilers can generate code for accelerators such as GPUs. Description of these capabilities is beyond the scope of this guide.

OpenMP

Add this flag to any of the above:  -mp

GNU

  NON-MPI MPI
FORTRAN 90 gfortran mpif90
C gcc mpicc
C++ g++ mpicxx

Recommended Optimization Options

The  -O2 -march=native  options are recommended with the GNU compilers. (For more options, see the "man" pages for the compilers)

OpenMP

Add this flag to any of the above:  -fopenmp

 

Ruby Compilers

Intel (recommended)

  NON-MPI MPI
FORTRAN 90 ifort mpif90
C icc mpicc
C++ icpc mpicxx

Recommended Optimization Options

The  -O2 -xHost  options are recommended with the Intel compilers. (For more options, see the "man" pages for the compilers.

OpenMP

Add this flag to any of the above: -qopenmp or -openmp

PGI

  NON-MPI MPI
FORTRAN 90 pgfortran  or  pgf90 mpif90
C pgcc mpicc
C++ pgc++ mpicxx
NOTE: The C++ compiler used to be pgCC, but newer versions of PGI do not support this name.

Recommended Optimization Options

The  -fast  option is appropriate with all PGI compilers. (For more options, see the "man" pages for the compilers)

Note: The PGI compilers can generate code for accelerators such as GPUs. Description of these capabilities is beyond the scope of this guide.

OpenMP

Add this flag to any of the above: -mp

GNU

  NON-MPI MPI
FORTRAN 90 gfortran mpif90
C gcc mpicc
C++ g++ mpicxx

Recommended Optimization Options

The -O2 -march=native  options are recommended with the GNU compilers. (For more options, see the "man" pages for the compilers)

OpenMP

Add this flag to any of the above: -fopenmp

 

Further Reading:

Intel Compiler Page

PGI Compiler Page

GNU Complier Page

Supercomputer: 
Technologies: 
Fields of Science: 

Firewall and Proxy Settings

Connections to OSC

In order for users to access OSC resources through the web your firewall rules should allow for connections to the following publicly-facing IP ranges.  Otherwise, users may be blocked or denied access to our services.

  • 192.148.248.0/24
  • 192.148.247.0/24
  • 192.157.5.0/25

The followingg TCP ports should be opened:

  • 80 (HTTP)
  • 443 (HTTPS)
  • 22 (SSH)

The following domain should be allowed:

  • *.osc.edu

Users may follow the instructions below "Test your configuration" to ensure that your system is not blocked from accessing our services. If you are still unsure of whether their network is blocking theses hosts or ports should contact their local IT administrator.

Test your configuration

[Windows] Test your connection using PuTTY

  1. Open the PuTTY application.
  2. Enter IP address listed in "Connections to OSC" in the "Host Name" field.
  3. Enter 22 in the "Port" field.
  4. Click the 'Telnet' radio button under "Connection Type".
  5. Click "Open" to test the connection.
  6. Confirm the response. If the connection is successful, you will see a message that says "SSH-2.0-OpenSSH_5.3", as shown below. If you receive a PuTTY error, consult your system administrator for network access troubleshooting.

putty

[OSX/Linux] Test your configuration using telnet

  1. Open a terminal.
  2. Type telnet IPaddress 22 (Here, IPaddress is IP address listed in "Connections to OSC").
  3. Confirm the connection. 

Connections from OSC

All outbound network traffic from all of OSC's compute nodes are routed through a network address translation host (NAT), or two backup servers:

  • nat.osc.edu (192.157.5.13)
  • 192.148.248.35
  • 192.148.248.186

IT and Network Administrators

Please use the above information in order to assit users in acessing our resources.  

Occasionally new services may be stood up using hosts and ports not described here.  If you believe our list needs correcting please let us know at oschelp@osc.edu.

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Job and storage charging

Ohio academics should visit the fee structure page for pricing information.
All others should contact OSC Sales for pricing information.
If there are questions/concerns on charging at OSC, please contact OSC Help.

Job charging based on usage

Jobs are charged based length, number of cores, amount of memory, single node versus multi-node, and type of resource.

Length and number of cores

Jobs are recorded in terms of core-hours hours used. Core-hours can be calculated by:

number of cores * length of job

e.g.

A 4 core job that runs for 2 hours would have a total core-hour usage of:

4 cores * 2 hours = 8 core-hours

Amount of Memory

Each processor has a default amount of memory paired along with it, which differs by cluster. When requesting a specifc amount of memory that doesn't correlate with the default pairing, the charging uses an algorithm to determine if the effective cores should be used.

The value for effective cores will be used in place of the actual cores used if and only if it is larger than the explicit number of cores requested.

effective cores = memory / memory per core

e.g.

A job that requests  nodes=1:ppn=3  will still be charged for 3 cores of usage.

However, a job that requests  nodes=1:ppn=1,mem=12GB, where the default memory allocated per core is 4GB, then the job will be charged for 3 cores worth of usage.

effective cores = 12GB / (4GB/core) = 3 core

Single versus Multi-Node

If requesting a single node, then a job is charged for only the cores/processors requested. However, when requesting multiple nodes the job is charged for each entire node regardless of the number of cores/processors requested.

Type of resource

Depending on the type of node requested, it can change the dollar rate charged per core-hour. There are currently three types of nodes, regular, hugememory,and gpu.

If a gpu node is used, there are two metrics recorded, core-hours and gpu-hours. Each has a different dollar-rate, and these are combined to determine the total charges for usage.

Ohio academics should visit the fee structure page for pricing information.
All others should contact OSC Sales for pricing information.

e.g.

A job requests nodes=1:ppn=8:gpus=2 and runs for 1 hour.

The usage charge would be calculated using:

8 cores * 1 hour = 8 core-hours

and

2 gpus * 1 hour = 2 gpu-hours

and combined for:

8 core-hours + 2 gpu-hours

Project storage charging based on quota

Projects that request extra storage be added are charged for that storage based on the total space reserved (i.e. your quota). 

The rates are in TB per month:

storage quota in TB * rate per month
Ohio academics should visit the fee structure page for pricing information.
All others should contact OSC Sales for pricing information.
Please contact OSC Help with questions/concerns.

Out-of-Memory (OOM) or Excessive Memory Usage

Problem description

A common problem on our systems is for a user job to run a node out of memory or to use more than its allocated share of memory if the node is shared with other jobs.

If a job exhausts both the physical memory and the swap space on a node, it causes the node to crash. With a parallel job, there may be many nodes that crash. When a node crashes, the systems staff has to manually reboot and clean up the node. If other jobs were running on the same node, the users have to be notified that their jobs failed.

If your job requests less than a full node, for example, -l nodes=1:ppn=1, it may be scheduled on a node with other running jobs. In this case, your job is entitled to a memory allocation proportional to the number of cores requested. For example, if a system has 4.5 GB per core and you request one core, it is your responsibility to make sure your job uses no more than 4.5 GB. Otherwise your job will interfere with the execution of other jobs.

The memory limit you set in PBS does not work the way one might expect it to. The only thing the -l mem=xxx flag is good for is requesting a large-memory node. It does not cause your job to be allocated the requested amount of memory, nor does it limit your job’s memory usage.

Background

Each node has a fixed amount of physical memory and a fixed amount of disk space designated as swap space. If your program and data don’t fit in physical memory, the virtual memory system writes pages from physical memory to disk as necessary and reads in the pages it needs. This is called swapping. 

You can find the amount of memory on our systems by following the links on our Supercomputers page. You can see the memory and swap values for a node by running the Linux command free on the node.

In the world of high-performance computing, swapping is almost always undesirable. If your program does a lot of swapping, it will spend most of its time doing disk I/O and won’t get much computation done. Therefore, swapping is not supported at OSC. You should consider the suggestions below.

Suggested solutions

Here are some suggestions for fixing jobs that use too much memory. Feel free to contact OSC Help for assistance with any of these options.

Some of these remedies involve requesting more processors (cores) for your job. As a general rule, we require you to request a number of processors proportional to the amount of memory you require. You need to think in terms of using some fraction of a node rather than treating processors and memory separately. If some of the processors remain idle, that’s not a problem. Memory is just as valuable a resource as processors.

Request whole node or more processors

Jobs requesting less than a whole node are those that for example have nodes=1 with ppn<40 on Pitzer (ppn<48 on Pitzer expansion):  nodes=1:ppn=1. These jobs can be problematic for two reasons. First, they are entitled to use an amount of memory proportional to the ppn value requested; if they use more they interfere with other jobs. Second, if they cause a node to crash, it typically affects multiple jobs and multiple users.

If you’re sure about your memory usage, it’s fine to request just the number of processors you need, as long as it’s enough to cover the amount of memory you need. If you’re not sure, play it safe and request all the processors on the node.

Reduce memory usage

Consider whether your job’s memory usage is reasonable in light of the work it’s doing. The code itself typically doesn’t require much memory, so you need to look mostly at the data size.

If you’re developing the code yourself, look for memory leaks. In MATLAB look for large arrays that can be cleared.

An out-of-core algorithm will typically use disk more efficiently than an in-memory algorithm that relies on swapping. Some third-party software gives you a choice of algorithms or allows you to set a limit on the memory the algorithm will use.

Use more nodes for a parallel job

If you have a parallel job you can get more total memory by requesting more nodes. Depending on the characteristics of your code you may also need to run fewer processes per node.

Here’s an example. Suppose your job on Pitzer includes the following lines:

#PBS -l nodes=2:ppn=40
…
mpiexec mycode

This job uses 2 nodes, so it has 2*178 GB=356 GB total memory available to it. The mpiexec command by default runs one process per core, which in this case is 2*40=80 copies of mycode.

If this job uses too much memory you can spread those 80 processes over more nodes. The following lines request 4 nodes, giving you a total of 4*178 GB=712 GB total memory. The -ppn 20 option on the mpiexec command says to run 20 processes per node instead of 40, for a total of 80 as before.

#PBS -l nodes=4:ppn=40
…
mpiexec -ppn 20 mycode

Since parallel jobs are always assigned whole nodes, the following lines will also run 20 processes per node on 4 nodes.

#PBS -l nodes=4:ppn=20
…
mpiexec mycode

Request large-memory nodes

Pitzer has four huge memory nodes with ~3 TB of memory and with 80 cores. Owens has sixteen huge memory nodes with ~1.5 TB of memory and with 48 cores.

Since there are so few of these nodes, compared to hundreds of standard nodes, jobs requesting them will often have a long wait in the queue. The wait will be worthwhile, though, if these nodes solve your memory problem. See this page on how to request huge memory node on Owens; see this page on how to request huge memory node on Pitzer. 

Some knowledge about virtual memory

The sections above are intended to help you get your job running correctly. This section is to provide some general knowledge about virtual memory. 

We will use Linux terminology. Each process has several virtual memory values associated with it. VmSize is virtual memory size; VmRSS is resident set size, or physical memory used; VmSwap is swap space used. The number we care about is the total memory used by the process, which is VmRSS + VmSwap. The relationship among VmSize, VmRSS, and VmSwap is:  VmSize >= VmRSS+VmSwap. For many programs, this bound is fairly tight; for others VmSize can be much larger than the memory actually used. If the bound is reasonably tight, -l vmem=4gb provides an effective mechanism for limiting memory usage to 4gb (for example). If the bound is not tight, VmSize may prevent the program from starting even if VmRSS+VmSwap would have been perfectly reasonable. Java and some FORTRAN 77 programs in particular have this problem.

What PBS allows a job to limit is VmRSS (using -l mem=xxx) or VmSize (using -l vmem=xxx). The vmem limit in PBS is for the entire job, not just one node, so it isn’t useful with parallel (multimode) jobs.

At OSC, however, we do not support the vmem limit option anymore. 

Feel free to contact OSC Help for assistance if you need to use vmem option, or have other situations that aren’t covered here. 

How to monitor your memory usage

qstat -f

While your job is running the command qstat -f jobid will tell you the peak physical and virtual memory usage of the job so far. For a parallel job, these numbers are the aggregate usage across all nodes of the job. The values reported by qstat may lag the true values by a couple of minutes.

free

For parallel (multinode) jobs you can check your per-node memory usage while your job is running by using pdsh -j jobid free -m.

ja

You can put the command ja (job accounting) at the end of your batch script to capture the resource usage reported by qstat -f. The information will be written to your job output log, job_name.o123456.

OnDemand

You can also view node status graphically using the OSC OnDemand Portal (ondemand.osc.edu).  Under "Jobs" select "Active Jobs". Click on "Job Status" and scroll down to see memory usage. This shows the total memory usage for the node; if your job is not the only one running there, it may be hard to interpret.

Below is a typical graph for jobs using too much memory (this is from a cluster that is no longer available; it had 12 cores and 48 GB per node). It shows two jobs that ran back-to-back on the same node. The first peak is a job that used all the available physical memory (blue) and a large amount of swap (purple). It completed successfully without crashing the node. The second job followed the same pattern but actually crashed the node.

Notes

If it appears that your job is close to crashing a node, we may preemptively delete the job.

If your job is interfering with other jobs by using more memory than it should be, we may delete the job.

In extreme cases OSC staff may restrict your ability to submit jobs. If you crash a large number of nodes or continue to submit problem jobs after we have notified you of the situation, this may be the only way to protect the system and our other users. If this happens, we will restore your privileges as soon as you demonstrate that you have resolved the problem.

For details on retrieving files from unexpectedly terminated jobs see this FAQ.

For assistance

OSC has staff available to help you resolve your memory issues. See our Support Services page for contact information.

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Service: 

XDMoD Tool

XDMoD Overview

XDMoD, which stands for XD Metrics on Demand, is an NSF-funded open source tool that provides a wide range of metrics pertaining to resource utilization and performance of high-performance computing (HPC) resources, and the impact these resources have in terms of scholarship and research.

How to log in

Visit OSC's XDMoD (xdmod.osc.edu) and click 'Sign In' in the upper left corner of the page.

screenshot of the XDMoD displaying the above text

A login window will appear. Click the button 'Login here.' under the 'Sign in with Ohio SuperComputer Center:', as shown below:
screenshot of the XDMoD displaying the above text
 
This redirects to a login page where one can use their OSC credentials to sign in.
screenshot of the XDMoD displaying the above text

XDMoD Tabs

When you first log in you will be directed to the Summary tab. The different XDMoD tabs are located near the top of the page. You will be able to change tabs simply by click on the one you would like to view. By default, you will see the data from the previous month, but you can change the start and end date and then click 'refresh' to update the timeframe being reported.

screenshot of the XDMoD displaying the above text

Summary:

The Summary tab is comprised of a duration selector toolbar, a summary information bar, followed by a select set of charts representative of the usage. The Summary tab provides a dashboard that presents summary statistics and selected charts that are useful to the role of the current user. More information can be found at the XDMoD User Manual

Usage:

The Usage tab is comprised of a chart selection tree on the left, and a chart viewer to the right of the page. The usage tab provides a convenient way to browse all the realms present in XDMoD. More information can be found at the XDMoD User Manual

Metric Explorer:

The Metric Explorer allows one to create complex plots containing multiple multiple metrics. It has many points and click features that allow the user to easily add, filter, and modify the data and the format in which it is presented. More information can be found at the XDMoD User Manual

App Kernels:

The Application Kernels tab consists of three sub-tabs, and each has a specific goal in order to make viewing application kernels simple and intuitive. The three sub-tabs consist of the Application Kernels Viewer, Application Kernels Explorer, and the Reports subsidiary tabs. More information can be found at the XDMoD User Manual

Report Generator:

This tab will allow you to manage reports. The left region provides a listing of any reports you have created. The right region displays any charts you have chosen to make available for building a report. More information can be found at the XDMoD User Manual

Job Viewer:

The Job Viewer tab displays information about individual HPC jobs and includes a search interface that allows jobs to be selected based on a wide range of filters. This tab also contains the SUPReMM module. More information on the SUPReMM module can be found below in this documentation. More information can be found at the XDMoD User Manual

About:

This tab will display information about XDMoD.

Different Roles

XDMoD utilizes roles to restrict access to data and elements of the user interface such as tabs. OSC client holds the 'User Role' by default after you log into OSC XDMoD using your OSC credentials. With 'User Role', users are able to view all data available to their personal utilization information. They are also able to view information regarding their allocations, quality of service data via the Application Kernel Explorer, and generate custom reports. We also support the 'Principal Investigator' role, who has access to all data available to a user, as well as detailed information for any users included on their allocations or project.

References, Resources, and Documentation

 

 

Supercomputer: 

Job Viewer

The Job Viewer Tab displays information about individual HPC jobs and includes a search interface that allows jobs to be selected based on a wide range of filters:

1. Click on the Job Viewer tab near the top of the page.

2. Click Search in the top left-hand corner of the page

screenshot of the XDMoD displaying the above text

     3. If you know the Resource and Job Number, use the quick search lookup form discussed in 4a. If you would like more options, use the advanced search discussed in 4b.

     4a. For a quick job lookup, select the resource and enter the job number and click 'Search'.

screenshot of the XDMoD displaying the above text

     4b. Within the Advanced Search form, select a timeframe and Add one or more filters. Click to run the search on the server.

screenshot of the XDMoD displaying the above text

     5. Select one or more Jobs. Provide the 'Search Name', and click 'Save Results' at the bottom of this window to view data about the selected jobs.

     6. To view data in more details for the selected job, under the Search History, click on the Tree and select a Job.

     7. More information can be found in the section of 'Job Viewer' of the XDMoD User Manual.

Supercomputer: 

XDMoD - Checking Job Efficiency

Intro

XDMoD can be used to look at the performance of past jobs. This tutorial will explain how to retreive this job performance data and how to use this data to best utilize OSC resources.

First, log into XDMoD.

See XDMoD Tool webpage for details about XDMoD and how to log in.

You will be sent to the Summary Tab in XDMoD:

Screen Shot 2019-03-28 at 11.04.53 AM.png

Click on the Metric Explorer tab, then navigate to the Metric Catalog click SUPREMM to show the various metric options, then Click the "Avg CPU %: User: weighted by core hour " metric.

A drop-down menu will appear for grouping the data to viewed. Group by "CPU User Value

Screen Shot 2019-04-03 at 2.15.23 PM_0.png":

 

This will provide a time-series chart showing the average 'CPU user % weighted by core hours, over all jobs that were executing' separated by groups of 10 for that 'CPU User value'.

Screen Shot 2019-04-03 at 2.21.10 PM.png

One can change the time period by adjusting the preset duration value or entering dates in the "start" and "end" boxes by selecting the calender or manually entering dates in the format 'yyyy-mm-dd'. Once the desired time period is entered the "Refresh" button will be highlighted yellow, click the "Refresh" button to reload that time period data into the chart.

Screen Shot 2019-03-28 at 11.38.25 AM.png

Once the data is loaded, click on one of the data points, then navigate to "Drilldown" and select "Job Wall Time". This will group the job data by the amount of wall time used.

Screen Shot 2019-04-03 at 2.28.30 PM.png

Generally, the lower the CPU User Value, the less efficient that job was. This chart can now be used to go into some detailed information on specific jobs. Click one of the points again and select "Show raw data".

Screen Shot 2019-03-28 at 3.24.50 PM.png

This will bring up a list of jobs included in that data point. Click one of the jobs shown.

Screen Shot 2019-03-28 at 3.25.21 PM.png

After loading, this brings up the "Job Viewer" Tab for showing the details about the job selected.

Screen Shot 2019-03-28 at 3.28.57 PM.png

It is important to explain some information about the values immediately visible such as the "CPU User", "CPU User Balance" and "Memory Headroom".

The "CPU User" section gives a ratio for the amount of CPU time used by the job during the time that job was executing, think of it as how much "work" the CPUs were doing doing execution.

Screen Shot 2019-03-28 at 3.32.30 PM.png

The "CPU User Balance" section gives a measure for how evenly spread the "work" was between all the CPUs that were allocated to this job while it was executing. (Work here means how well was the CPU utilized, and it is preferred that the CPUs be close to fully utilized during job execution.)

Screen Shot 2019-03-28 at 3.32.44 PM.png

Finally, "Memory Headroom" gives a measure for the amount of memory used for that job. It can be difficult to understand what a good value is here. Generally, it is recommended to not specifically request an amount of memory unless the job requires it. When making those memory requests, it can be beneficial to investigate the amount of memory that is actually used by the job and plan accordingly. Below, a value closer to 0 means a job used most of the memory allocated to it and a value closer to 1 means that the job used less memory than the job was allocated.

Screen Shot 2019-03-28 at 3.32.55 PM.png

This information is useful for better utilizing OSC resources by having better estimates of the resources that jobs may require.